diff --git a/shortcuts/mail/draft/htmltext.go b/shortcuts/mail/draft/htmltext.go
index 0ef9c17de..fbaa585a8 100644
--- a/shortcuts/mail/draft/htmltext.go
+++ b/shortcuts/mail/draft/htmltext.go
@@ -123,6 +123,13 @@ func isHTMLBlockBoundary(n *xhtml.Node) bool {
 	}
 }
 
+// PlainTextFromHTML is the exported wrapper over plainTextFromHTML, so the
+// mail package can render an HTML signature as a plain-text fallback when a
+// message body is sent in plain-text mode. The conversion logic is unchanged.
+func PlainTextFromHTML(raw string) string {
+	return plainTextFromHTML(raw)
+}
+
 // bodyLooksLikeHTML reports whether raw appears to contain HTML markup.
 // This is intentionally heuristic: it exists to reject obvious plain-text
 // input when a draft's authored body is text/html.
diff --git a/shortcuts/mail/draft/htmltext_test.go b/shortcuts/mail/draft/htmltext_test.go
index f640016b5..8d7e1bb0a 100644
--- a/shortcuts/mail/draft/htmltext_test.go
+++ b/shortcuts/mail/draft/htmltext_test.go
@@ -102,3 +102,10 @@ func TestIsHTMLNonTextTag(t *testing.T) {
 		})
 	}
 }
+
+func TestPlainTextFromHTMLExported(t *testing.T) {
+	got := PlainTextFromHTML("<p>Hello world</p>")
+	if !strings.Contains(got, "Hello world") {
+		t.Fatalf("PlainTextFromHTML: expected to contain \"Hello world\", got %q", got)
+	}
+}
diff --git a/shortcuts/mail/mail_draft_create.go b/shortcuts/mail/mail_draft_create.go
index 8f4875c8b..316029193 100644
--- a/shortcuts/mail/mail_draft_create.go
+++ b/shortcuts/mail/mail_draft_create.go
@@ -56,6 +56,7 @@ var MailDraftCreate = common.Shortcut{
 		{Name: "request-receipt", Type: "bool", Desc: "Request a read receipt (Message Disposition Notification, RFC 3798) addressed to the sender. Recipient mail clients may prompt the user, send automatically, or silently ignore — delivery of a receipt is not guaranteed."},
 		{Name: "template-id", Desc: "Optional. Apply a saved template by ID (decimal integer string) before composing. The template's subject/body/to/cc/bcc/attachments are merged with user-supplied flags (user flags win). Requires --as user."},
 		signatureFlag,
+		noSignatureFlag,
 		priorityFlag,
 		eventSummaryFlag, eventStartFlag, eventEndFlag, eventLocationFlag,
 		showLintDetailsFlag,
@@ -92,7 +93,7 @@ var MailDraftCreate = common.Shortcut{
 		if !hasTemplate && strings.TrimSpace(runtime.Str("subject")) == "" {
 			return mailValidationParamError("--subject", "--subject is required; pass the final email subject (or use --template-id)")
 		}
-		if err := validateSignatureWithPlainText(runtime.Bool("plain-text"), runtime.Str("signature-id")); err != nil {
+		if err := validateNoSignatureConflict(runtime.Bool("no-signature"), runtime.Str("signature-id")); err != nil {
 			return err
 		}
 		if err := validateEventFlags(runtime); err != nil {
@@ -180,12 +181,22 @@ var MailDraftCreate = common.Shortcut{
 		if strings.TrimSpace(input.Body) == "" {
 			return mailValidationParamError("--body", "effective body is empty after applying template; pass --body explicitly")
 		}
-		sigResult, err := resolveSignature(ctx, runtime, mailboxID, runtime.Str("signature-id"), runtime.Str("from"))
+		signatureID := runtime.Str("signature-id")
+		noSignature := runtime.Bool("no-signature")
+		senderEmail := resolveComposeSenderEmail(runtime)
+		// Auto-resolve default signature when neither --no-signature nor --signature-id is set.
+		if noSignature {
+			signatureID = ""
+		} else if signatureID == "" {
+			signatureID = autoResolveSignatureID(runtime, mailboxID, senderEmail, false)
+		}
+		sigResult, err := resolveSignature(ctx, runtime, mailboxID, signatureID, senderEmail,
+			runtime.Str("signature-id") != "", !input.PlainText)
 		if err != nil {
 			return err
 		}
 		rawEML, lintApplied, lintBlocked, err := buildRawEMLForDraftCreate(ctx, runtime, input, sigResult, priority,
-			templateLargeAttachmentIDs, mailboxID, templateID, templateInlineAttachments, templateSmallAttachments)
+			templateLargeAttachmentIDs, mailboxID, templateID, templateInlineAttachments, templateSmallAttachments, senderEmail)
 		if err != nil {
 			return err
 		}
@@ -241,13 +252,19 @@ func buildRawEMLForDraftCreate(
 	mailboxID, templateID string,
 	templateInlineAttachments []templateInlineRef,
 	templateSmallAttachments []templateAttachmentRef,
+	senderEmailHint string,
 ) (rawEMLOut string, lintApplied, lintBlocked []lint.Finding, err error) {
 	// Initialise lint findings as empty (non-nil) slices so callers can
 	// surface them through the envelope unconditionally even on the
 	// plain-text branch.
 	lintApplied, lintBlocked = emptyLintFindings()
 
-	senderEmail := resolveComposeSenderEmail(runtime)
+	// Use the pre-resolved senderEmail when available (avoids a duplicate
+	// profile API call when Execute already fetched it for auto-resolve).
+	senderEmail := senderEmailHint
+	if senderEmail == "" {
+		senderEmail = resolveComposeSenderEmail(runtime)
+	}
 	if senderEmail == "" {
 		return "", lintApplied, lintBlocked, mailValidationParamError("--from", "unable to determine sender email; please specify --from explicitly")
 	}
@@ -290,7 +307,7 @@ func buildRawEMLForDraftCreate(
 	var composedHTMLBody string
 	var composedTextBody string
 	if input.PlainText {
-		composedTextBody = input.Body
+		composedTextBody = injectPlainTextSignature(input.Body, sigResult)
 		bld = bld.TextBody([]byte(composedTextBody))
 	} else if bodyIsHTML(input.Body) || sigResult != nil {
 		htmlBody := input.Body
diff --git a/shortcuts/mail/mail_draft_create_test.go b/shortcuts/mail/mail_draft_create_test.go
index 21cbf9304..1b78e2535 100644
--- a/shortcuts/mail/mail_draft_create_test.go
+++ b/shortcuts/mail/mail_draft_create_test.go
@@ -62,7 +62,7 @@ func TestBuildRawEMLForDraftCreate_ResolvesLocalImages(t *testing.T) {
 		Body:    `<p>Hello</p><p><img src="./test_image.png" /></p>`,
 	}
 
-	rawEML, _, _, err := buildRawEMLForDraftCreate(context.Background(), newRuntimeWithFrom("sender@example.com"), input, nil, "", nil, "", "", nil, nil)
+	rawEML, _, _, err := buildRawEMLForDraftCreate(context.Background(), newRuntimeWithFrom("sender@example.com"), input, nil, "", nil, "", "", nil, nil, "")
 	if err != nil {
 		t.Fatalf("buildRawEMLForDraftCreate() error = %v", err)
 	}
@@ -88,7 +88,7 @@ func TestBuildRawEMLForDraftCreate_NoLocalImages(t *testing.T) {
 		Body:    `<p>Hello <b>world</b></p>`,
 	}
 
-	rawEML, _, _, err := buildRawEMLForDraftCreate(context.Background(), newRuntimeWithFrom("sender@example.com"), input, nil, "", nil, "", "", nil, nil)
+	rawEML, _, _, err := buildRawEMLForDraftCreate(context.Background(), newRuntimeWithFrom("sender@example.com"), input, nil, "", nil, "", "", nil, nil, "")
 	if err != nil {
 		t.Fatalf("buildRawEMLForDraftCreate() error = %v", err)
 	}
@@ -124,7 +124,7 @@ func TestBuildRawEMLForDraftCreate_AutoResolveCountedInSizeLimit(t *testing.T) {
 		Attach:  "./big.txt",
 	}
 
-	_, _, _, err := buildRawEMLForDraftCreate(context.Background(), newRuntimeWithFrom("sender@example.com"), input, nil, "", nil, "", "", nil, nil)
+	_, _, _, err := buildRawEMLForDraftCreate(context.Background(), newRuntimeWithFrom("sender@example.com"), input, nil, "", nil, "", "", nil, nil, "")
 	if err == nil {
 		t.Fatal("expected size limit error when auto-resolved image + attachment exceed 25MB")
 	}
@@ -145,7 +145,7 @@ func TestBuildRawEMLForDraftCreate_OrphanedInlineSpecError(t *testing.T) {
 		Inline:  `[{"cid":"orphan","file_path":"./unused.png"}]`,
 	}
 
-	_, _, _, err := buildRawEMLForDraftCreate(context.Background(), newRuntimeWithFrom("sender@example.com"), input, nil, "", nil, "", "", nil, nil)
+	_, _, _, err := buildRawEMLForDraftCreate(context.Background(), newRuntimeWithFrom("sender@example.com"), input, nil, "", nil, "", "", nil, nil, "")
 	if err == nil {
 		t.Fatal("expected error for orphaned --inline CID not referenced in body")
 	}
@@ -166,7 +166,7 @@ func TestBuildRawEMLForDraftCreate_MissingCIDRefError(t *testing.T) {
 		Inline:  `[{"cid":"present","file_path":"./present.png"}]`,
 	}
 
-	_, _, _, err := buildRawEMLForDraftCreate(context.Background(), newRuntimeWithFrom("sender@example.com"), input, nil, "", nil, "", "", nil, nil)
+	_, _, _, err := buildRawEMLForDraftCreate(context.Background(), newRuntimeWithFrom("sender@example.com"), input, nil, "", nil, "", "", nil, nil, "")
 	if err == nil {
 		t.Fatal("expected error for missing CID reference")
 	}
@@ -183,7 +183,7 @@ func TestBuildRawEMLForDraftCreate_WithPriority(t *testing.T) {
 		Body:    `<p>Hello</p>`,
 	}
 
-	rawEML, _, _, err := buildRawEMLForDraftCreate(context.Background(), newRuntimeWithFrom("sender@example.com"), input, nil, "1", nil, "", "", nil, nil)
+	rawEML, _, _, err := buildRawEMLForDraftCreate(context.Background(), newRuntimeWithFrom("sender@example.com"), input, nil, "1", nil, "", "", nil, nil, "")
 	if err != nil {
 		t.Fatalf("buildRawEMLForDraftCreate() error = %v", err)
 	}
@@ -201,7 +201,7 @@ func TestBuildRawEMLForDraftCreate_NoPriority(t *testing.T) {
 		Body:    `<p>Hello</p>`,
 	}
 
-	rawEML, _, _, err := buildRawEMLForDraftCreate(context.Background(), newRuntimeWithFrom("sender@example.com"), input, nil, "", nil, "", "", nil, nil)
+	rawEML, _, _, err := buildRawEMLForDraftCreate(context.Background(), newRuntimeWithFrom("sender@example.com"), input, nil, "", nil, "", "", nil, nil, "")
 	if err != nil {
 		t.Fatalf("buildRawEMLForDraftCreate() error = %v", err)
 	}
@@ -237,7 +237,7 @@ func TestBuildRawEMLForDraftCreate_RequestReceiptAddsHeader(t *testing.T) {
 	}
 
 	rawEML, _, _, err := buildRawEMLForDraftCreate(context.Background(),
-		newRuntimeWithFromAndRequestReceipt("sender@example.com", true), input, nil, "", nil, "", "", nil, nil)
+		newRuntimeWithFromAndRequestReceipt("sender@example.com", true), input, nil, "", nil, "", "", nil, nil, "")
 	if err != nil {
 		t.Fatalf("buildRawEMLForDraftCreate() error = %v", err)
 	}
@@ -260,7 +260,7 @@ func TestBuildRawEMLForDraftCreate_RequestReceiptOmittedByDefault(t *testing.T)
 	}
 
 	rawEML, _, _, err := buildRawEMLForDraftCreate(context.Background(),
-		newRuntimeWithFromAndRequestReceipt("sender@example.com", false), input, nil, "", nil, "", "", nil, nil)
+		newRuntimeWithFromAndRequestReceipt("sender@example.com", false), input, nil, "", nil, "", "", nil, nil, "")
 	if err != nil {
 		t.Fatalf("buildRawEMLForDraftCreate() error = %v", err)
 	}
@@ -283,7 +283,7 @@ func TestBuildRawEMLForDraftCreate_PlainTextSkipsResolve(t *testing.T) {
 		PlainText: true,
 	}
 
-	rawEML, _, _, err := buildRawEMLForDraftCreate(context.Background(), newRuntimeWithFrom("sender@example.com"), input, nil, "", nil, "", "", nil, nil)
+	rawEML, _, _, err := buildRawEMLForDraftCreate(context.Background(), newRuntimeWithFrom("sender@example.com"), input, nil, "", nil, "", "", nil, nil, "")
 	if err != nil {
 		t.Fatalf("buildRawEMLForDraftCreate() error = %v", err)
 	}
@@ -304,7 +304,7 @@ func TestBuildRawEMLForDraftCreate_WithCalendarEvent(t *testing.T) {
 		Body:    "<p>Please join us</p>",
 	}
 
-	rawEML, _, _, err := buildRawEMLForDraftCreate(context.Background(), rt, input, nil, "", nil, "", "", nil, nil)
+	rawEML, _, _, err := buildRawEMLForDraftCreate(context.Background(), rt, input, nil, "", nil, "", "", nil, nil, "")
 	if err != nil {
 		t.Fatalf("buildRawEMLForDraftCreate() error = %v", err)
 	}
diff --git a/shortcuts/mail/mail_draft_edit.go b/shortcuts/mail/mail_draft_edit.go
index 76a6f9f9c..0bfbf998a 100644
--- a/shortcuts/mail/mail_draft_edit.go
+++ b/shortcuts/mail/mail_draft_edit.go
@@ -134,7 +134,7 @@ var MailDraftEdit = common.Shortcut{
 		for i := range patch.Ops {
 			switch patch.Ops[i].Op {
 			case "insert_signature":
-				sigResult, sigErr := resolveSignature(ctx, runtime, mailboxID, patch.Ops[i].SignatureID, draftFromEmail)
+				sigResult, sigErr := resolveSignature(ctx, runtime, mailboxID, patch.Ops[i].SignatureID, draftFromEmail, true, true)
 				if sigErr != nil {
 					return sigErr
 				}
diff --git a/shortcuts/mail/mail_forward.go b/shortcuts/mail/mail_forward.go
index 25a0ff0ad..20a14577a 100644
--- a/shortcuts/mail/mail_forward.go
+++ b/shortcuts/mail/mail_forward.go
@@ -45,6 +45,7 @@ var MailForward = common.Shortcut{
 		{Name: "subject", Desc: "Optional. Override the auto-generated Fw: subject. When set, the shortcut uses this value verbatim instead of prefixing the original subject."},
 		{Name: "template-id", Desc: "Optional. Apply a saved template by ID (decimal integer string) before composing. The template's body/to/cc/bcc/attachments are merged into the forward draft (template values appended to user flags / forward-derived values; no de-duplication)."},
 		signatureFlag,
+		noSignatureFlag,
 		priorityFlag,
 		eventSummaryFlag, eventStartFlag, eventEndFlag, eventLocationFlag,
 		showLintDetailsFlag},
@@ -96,7 +97,7 @@ var MailForward = common.Shortcut{
 				return err
 			}
 		}
-		if err := validateSignatureWithPlainText(runtime.Bool("plain-text"), runtime.Str("signature-id")); err != nil {
+		if err := validateNoSignatureConflict(runtime.Bool("no-signature"), runtime.Str("signature-id")); err != nil {
 			return err
 		}
 		if err := validateEventFlags(runtime); err != nil {
@@ -127,12 +128,7 @@ var MailForward = common.Shortcut{
 			return err
 		}
 
-		signatureID := runtime.Str("signature-id")
 		mailboxID := resolveComposeMailboxID(runtime)
-		sigResult, sigErr := resolveSignature(ctx, runtime, mailboxID, signatureID, runtime.Str("from"))
-		if sigErr != nil {
-			return sigErr
-		}
 		sourceMsg, err := fetchComposeSourceMessage(runtime, mailboxID, messageId)
 		if err != nil {
 			return mailDecorateProblemMessage(err, "failed to fetch original message")
@@ -156,6 +152,18 @@ var MailForward = common.Shortcut{
 			senderEmail = orig.headTo
 		}
 
+		// Signature ID is resolved here (after senderEmail is finalised) so DefaultReplyID
+		// matches the correct usage. The actual image download in resolveSignature is deferred
+		// to after applyTemplate so the final plainText value (which a template can override
+		// via IsPlainTextMode) is used for the downloadImages decision.
+		signatureID := runtime.Str("signature-id")
+		noSignature := runtime.Bool("no-signature")
+		if noSignature {
+			signatureID = ""
+		} else if signatureID == "" {
+			signatureID = autoResolveSignatureID(runtime, mailboxID, senderEmail, true /*isReply*/)
+		}
+
 		// --template-id merge (§5.5 Q1-Q5).
 		var templateLargeAttachmentIDs []string
 		var templateInlineAttachments []templateInlineRef
@@ -198,6 +206,14 @@ var MailForward = common.Shortcut{
 				"bccs_count":         countAddresses(bccFlag),
 			})
 		}
+		// Resolve signature after template processing so plainText reflects any IsPlainTextMode
+		// override from the template. This avoids downloading HTML signature images when the
+		// template forces plain-text mode, which could cause CDN 403/5xx or timeout errors.
+		sigResult, sigErr := resolveSignature(ctx, runtime, mailboxID, signatureID, senderEmail,
+			runtime.Str("signature-id") != "", !plainText)
+		if sigErr != nil {
+			return sigErr
+		}
 		subjectOverride := strings.TrimSpace(runtime.Str("subject"))
 
 		// Post-merge recipient check for --confirm-send + --template-id:
@@ -310,7 +326,7 @@ var MailForward = common.Shortcut{
 				return err
 			}
 		} else {
-			composedTextBody = buildForwardedMessage(&orig, body)
+			composedTextBody = buildForwardedMessage(&orig, injectPlainTextSignature(body, sigResult))
 			bld = bld.TextBody([]byte(composedTextBody))
 		}
 		// Embed template SMALL non-inline attachments regardless of body mode.
diff --git a/shortcuts/mail/mail_reply.go b/shortcuts/mail/mail_reply.go
index d4f190894..11acea385 100644
--- a/shortcuts/mail/mail_reply.go
+++ b/shortcuts/mail/mail_reply.go
@@ -42,6 +42,7 @@ var MailReply = common.Shortcut{
 		{Name: "subject", Desc: "Optional. Override the auto-generated Re: subject. When set, the shortcut uses this value verbatim instead of prefixing the original subject."},
 		{Name: "template-id", Desc: "Optional. Apply a saved template by ID (decimal integer string) before composing. The template's body/to/cc/bcc/attachments are appended to the reply-derived values (no de-duplication; see warning in Execute output)."},
 		signatureFlag,
+		noSignatureFlag,
 		priorityFlag,
 		eventSummaryFlag, eventStartFlag, eventEndFlag, eventLocationFlag,
 		showLintDetailsFlag},
@@ -93,7 +94,7 @@ var MailReply = common.Shortcut{
 		if err := validateSendTime(runtime); err != nil {
 			return err
 		}
-		if err := validateSignatureWithPlainText(runtime.Bool("plain-text"), runtime.Str("signature-id")); err != nil {
+		if err := validateNoSignatureConflict(runtime.Bool("no-signature"), runtime.Str("signature-id")); err != nil {
 			return err
 		}
 		if err := validateEventFlags(runtime); err != nil {
@@ -129,12 +130,7 @@ var MailReply = common.Shortcut{
 			return err
 		}
 
-		signatureID := runtime.Str("signature-id")
 		mailboxID := resolveComposeMailboxID(runtime)
-		sigResult, sigErr := resolveSignature(ctx, runtime, mailboxID, signatureID, runtime.Str("from"))
-		if sigErr != nil {
-			return sigErr
-		}
 		sourceMsg, err := fetchComposeSourceMessage(runtime, mailboxID, messageId)
 		if err != nil {
 			return mailDecorateProblemMessage(err, "failed to fetch original message")
@@ -156,6 +152,18 @@ var MailReply = common.Shortcut{
 			senderEmail = orig.headTo
 		}
 
+		// Signature ID is resolved here (after senderEmail is finalised) so DefaultReplyID
+		// matches the correct usage. The actual image download in resolveSignature is deferred
+		// to after applyTemplate so the final plainText value (which a template can override
+		// via IsPlainTextMode) is used for the downloadImages decision.
+		signatureID := runtime.Str("signature-id")
+		noSignature := runtime.Bool("no-signature")
+		if noSignature {
+			signatureID = ""
+		} else if signatureID == "" {
+			signatureID = autoResolveSignatureID(runtime, mailboxID, senderEmail, true /*isReply*/)
+		}
+
 		replyTo := orig.replyTo
 		if replyTo == "" {
 			replyTo = orig.headFrom
@@ -208,6 +216,14 @@ var MailReply = common.Shortcut{
 				"bccs_count":         countAddresses(bccFlag),
 			})
 		}
+		// Resolve signature after template processing so plainText reflects any IsPlainTextMode
+		// override from the template. This avoids downloading HTML signature images when the
+		// template forces plain-text mode, which could cause CDN 403/5xx or timeout errors.
+		sigResult, sigErr := resolveSignature(ctx, runtime, mailboxID, signatureID, senderEmail,
+			runtime.Str("signature-id") != "", !plainText)
+		if sigErr != nil {
+			return sigErr
+		}
 		// --subject (explicit override) takes precedence over auto-generated.
 		subjectOverride := strings.TrimSpace(runtime.Str("subject"))
 
@@ -311,7 +327,7 @@ var MailReply = common.Shortcut{
 				return err
 			}
 		} else {
-			composedTextBody = bodyStr + quoted
+			composedTextBody = injectPlainTextSignature(bodyStr, sigResult) + quoted
 			bld = bld.TextBody([]byte(composedTextBody))
 		}
 		// Embed template SMALL non-inline attachments regardless of body mode.
diff --git a/shortcuts/mail/mail_reply_all.go b/shortcuts/mail/mail_reply_all.go
index 66f584e1f..3c2d19bef 100644
--- a/shortcuts/mail/mail_reply_all.go
+++ b/shortcuts/mail/mail_reply_all.go
@@ -43,6 +43,7 @@ var MailReplyAll = common.Shortcut{
 		{Name: "subject", Desc: "Optional. Override the auto-generated Re: subject. When set, the shortcut uses this value verbatim instead of prefixing the original subject."},
 		{Name: "template-id", Desc: "Optional. Apply a saved template by ID (decimal integer string) before composing. The template's body/to/cc/bcc/attachments are appended to the reply-derived values (no de-duplication; see warning in Execute output)."},
 		signatureFlag,
+		noSignatureFlag,
 		priorityFlag,
 		eventSummaryFlag, eventStartFlag, eventEndFlag, eventLocationFlag,
 		showLintDetailsFlag},
@@ -94,7 +95,7 @@ var MailReplyAll = common.Shortcut{
 		if err := validateSendTime(runtime); err != nil {
 			return err
 		}
-		if err := validateSignatureWithPlainText(runtime.Bool("plain-text"), runtime.Str("signature-id")); err != nil {
+		if err := validateNoSignatureConflict(runtime.Bool("no-signature"), runtime.Str("signature-id")); err != nil {
 			return err
 		}
 		if err := validateEventFlags(runtime); err != nil {
@@ -131,12 +132,7 @@ var MailReplyAll = common.Shortcut{
 			return err
 		}
 
-		signatureID := runtime.Str("signature-id")
 		mailboxID := resolveComposeMailboxID(runtime)
-		sigResult, sigErr := resolveSignature(ctx, runtime, mailboxID, signatureID, runtime.Str("from"))
-		if sigErr != nil {
-			return sigErr
-		}
 		sourceMsg, err := fetchComposeSourceMessage(runtime, mailboxID, messageId)
 		if err != nil {
 			return mailDecorateProblemMessage(err, "failed to fetch original message")
@@ -158,6 +154,18 @@ var MailReplyAll = common.Shortcut{
 			senderEmail = orig.headTo
 		}
 
+		// Signature ID is resolved here (after senderEmail is finalised) so DefaultReplyID
+		// matches the correct usage. The actual image download in resolveSignature is deferred
+		// to after applyTemplate so the final plainText value (which a template can override
+		// via IsPlainTextMode) is used for the downloadImages decision.
+		signatureID := runtime.Str("signature-id")
+		noSignature := runtime.Bool("no-signature")
+		if noSignature {
+			signatureID = ""
+		} else if signatureID == "" {
+			signatureID = autoResolveSignatureID(runtime, mailboxID, senderEmail, true /*isReply*/)
+		}
+
 		var removeList []string
 		for _, r := range strings.Split(removeFlag, ",") {
 			if s := strings.TrimSpace(r); s != "" {
@@ -218,6 +226,14 @@ var MailReplyAll = common.Shortcut{
 				"bccs_count":         countAddresses(bccFlag),
 			})
 		}
+		// Resolve signature after template processing so plainText reflects any IsPlainTextMode
+		// override from the template. This avoids downloading HTML signature images when the
+		// template forces plain-text mode, which could cause CDN 403/5xx or timeout errors.
+		sigResult, sigErr := resolveSignature(ctx, runtime, mailboxID, signatureID, senderEmail,
+			runtime.Str("signature-id") != "", !plainText)
+		if sigErr != nil {
+			return sigErr
+		}
 		subjectOverride := strings.TrimSpace(runtime.Str("subject"))
 
 		if err := validateRecipientCount(toList, ccList, bccFlag); err != nil {
@@ -316,7 +332,7 @@ var MailReplyAll = common.Shortcut{
 				return err
 			}
 		} else {
-			composedTextBody = bodyStr + quoted
+			composedTextBody = injectPlainTextSignature(bodyStr, sigResult) + quoted
 			bld = bld.TextBody([]byte(composedTextBody))
 		}
 		// Embed template SMALL non-inline attachments regardless of body mode.
diff --git a/shortcuts/mail/mail_send.go b/shortcuts/mail/mail_send.go
index b536aa827..fde49ac40 100644
--- a/shortcuts/mail/mail_send.go
+++ b/shortcuts/mail/mail_send.go
@@ -40,6 +40,7 @@ var MailSend = common.Shortcut{
 		{Name: "request-receipt", Type: "bool", Desc: "Request a read receipt (Message Disposition Notification, RFC 3798) addressed to the sender. Recipient mail clients may prompt the user, send automatically, or silently ignore — delivery of a receipt is not guaranteed."},
 		{Name: "template-id", Desc: "Optional. Apply a saved template by ID (decimal integer string) before composing. The template's subject/body/to/cc/bcc/attachments are merged with user-supplied flags (user flags win). Requires --as user."},
 		signatureFlag,
+		noSignatureFlag,
 		priorityFlag,
 		eventSummaryFlag, eventStartFlag, eventEndFlag, eventLocationFlag,
 		showLintDetailsFlag},
@@ -98,7 +99,7 @@ var MailSend = common.Shortcut{
 		if err := validateSendTime(runtime); err != nil {
 			return err
 		}
-		if err := validateSignatureWithPlainText(runtime.Bool("plain-text"), runtime.Str("signature-id")); err != nil {
+		if err := validateNoSignatureConflict(runtime.Bool("no-signature"), runtime.Str("signature-id")); err != nil {
 			return err
 		}
 		// Resolve the body content first (reading --body-file if set) so
@@ -145,6 +146,14 @@ var MailSend = common.Shortcut{
 
 		mailboxID := resolveComposeMailboxID(runtime)
 
+		// Auto-resolve default signature when neither --no-signature nor --signature-id is set.
+		noSignature := runtime.Bool("no-signature")
+		if noSignature {
+			signatureID = ""
+		} else if signatureID == "" {
+			signatureID = autoResolveSignatureID(runtime, mailboxID, senderEmail, false)
+		}
+
 		// --template-id merge: fetch template and apply it to compose state.
 		var templateLargeAttachmentIDs []string
 		var templateInlineAttachments []templateInlineRef
@@ -195,7 +204,8 @@ var MailSend = common.Shortcut{
 			}
 		}
 
-		sigResult, err := resolveSignature(ctx, runtime, mailboxID, signatureID, senderEmail)
+		sigResult, err := resolveSignature(ctx, runtime, mailboxID, signatureID, senderEmail,
+			runtime.Str("signature-id") != "", !plainText)
 		if err != nil {
 			return err
 		}
@@ -230,7 +240,7 @@ var MailSend = common.Shortcut{
 		// `lint_applied[]` / `original_blocked[]` even on the plain-text path.
 		lintApplied, lintBlocked := emptyLintEnvelopeFields()
 		if plainText {
-			composedTextBody = body
+			composedTextBody = injectPlainTextSignature(body, sigResult)
 			bld = bld.TextBody([]byte(composedTextBody))
 		} else if bodyIsHTML(body) || sigResult != nil {
 			// If signature is requested on plain-text body, auto-upgrade to HTML.
diff --git a/shortcuts/mail/signature/provider.go b/shortcuts/mail/signature/provider.go
index b5a807cc2..d07c0b726 100644
--- a/shortcuts/mail/signature/provider.go
+++ b/shortcuts/mail/signature/provider.go
@@ -6,6 +6,7 @@ package signature
 import (
 	"encoding/json"
 	"net/url"
+	"strings"
 
 	"github.com/larksuite/cli/errs"
 	"github.com/larksuite/cli/shortcuts/common"
@@ -55,6 +56,33 @@ func List(runtime *common.RuntimeContext, mailboxID string) ([]Signature, error)
 	return resp.Signatures, nil
 }
 
+// DefaultSendID returns the default send-mail signature ID for the given
+// sender email address. Returns "" if no default is configured.
+// "0" and empty string are treated as "no default" (API convention).
+func DefaultSendID(usages []SignatureUsage, emailAddr string) string {
+	for _, u := range usages {
+		if strings.EqualFold(u.EmailAddress, emailAddr) {
+			if u.SendMailSignatureID != "" && u.SendMailSignatureID != "0" {
+				return u.SendMailSignatureID
+			}
+		}
+	}
+	return ""
+}
+
+// DefaultReplyID returns the default reply/forward signature ID for the given
+// sender email address. Returns "" if no default is configured.
+func DefaultReplyID(usages []SignatureUsage, emailAddr string) string {
+	for _, u := range usages {
+		if strings.EqualFold(u.EmailAddress, emailAddr) {
+			if u.ReplySignatureID != "" && u.ReplySignatureID != "0" {
+				return u.ReplySignatureID
+			}
+		}
+	}
+	return ""
+}
+
 // Get returns a single signature by ID. Returns an error if not found.
 func Get(runtime *common.RuntimeContext, mailboxID, signatureID string) (*Signature, error) {
 	resp, err := ListAll(runtime, mailboxID)
diff --git a/shortcuts/mail/signature/provider_test.go b/shortcuts/mail/signature/provider_test.go
new file mode 100644
index 000000000..bc30213d6
--- /dev/null
+++ b/shortcuts/mail/signature/provider_test.go
@@ -0,0 +1,92 @@
+// Copyright (c) 2026 Lark Technologies Pte. Ltd.
+// SPDX-License-Identifier: MIT
+
+package signature
+
+import (
+	"testing"
+)
+
+func TestDefaultSendID_Match(t *testing.T) {
+	usages := []SignatureUsage{
+		{EmailAddress: "user@example.com", SendMailSignatureID: "sig-send-1", ReplySignatureID: "sig-reply-1"},
+	}
+	if got := DefaultSendID(usages, "user@example.com"); got != "sig-send-1" {
+		t.Fatalf("expected sig-send-1, got %q", got)
+	}
+}
+
+func TestDefaultSendID_CaseInsensitive(t *testing.T) {
+	usages := []SignatureUsage{
+		{EmailAddress: "User@Example.COM", SendMailSignatureID: "sig-send-x"},
+	}
+	if got := DefaultSendID(usages, "user@example.com"); got != "sig-send-x" {
+		t.Fatalf("expected case-insensitive match, got %q", got)
+	}
+}
+
+func TestDefaultSendID_NoMatch(t *testing.T) {
+	usages := []SignatureUsage{
+		{EmailAddress: "other@example.com", SendMailSignatureID: "sig-other"},
+	}
+	if got := DefaultSendID(usages, "user@example.com"); got != "" {
+		t.Fatalf("expected empty string for no match, got %q", got)
+	}
+}
+
+func TestDefaultSendID_ZeroIDTreatedAsNone(t *testing.T) {
+	usages := []SignatureUsage{
+		{EmailAddress: "user@example.com", SendMailSignatureID: "0"},
+	}
+	if got := DefaultSendID(usages, "user@example.com"); got != "" {
+		t.Fatalf("expected empty string for ID=0, got %q", got)
+	}
+}
+
+func TestDefaultSendID_NilUsages(t *testing.T) {
+	if got := DefaultSendID(nil, "user@example.com"); got != "" {
+		t.Fatalf("expected empty string for nil usages, got %q", got)
+	}
+}
+
+func TestDefaultReplyID_Match(t *testing.T) {
+	usages := []SignatureUsage{
+		{EmailAddress: "user@example.com", SendMailSignatureID: "sig-send-1", ReplySignatureID: "sig-reply-2"},
+	}
+	if got := DefaultReplyID(usages, "user@example.com"); got != "sig-reply-2" {
+		t.Fatalf("expected sig-reply-2, got %q", got)
+	}
+}
+
+func TestDefaultReplyID_CaseInsensitive(t *testing.T) {
+	usages := []SignatureUsage{
+		{EmailAddress: "User@Example.COM", ReplySignatureID: "sig-reply-x"},
+	}
+	if got := DefaultReplyID(usages, "user@example.com"); got != "sig-reply-x" {
+		t.Fatalf("expected case-insensitive match, got %q", got)
+	}
+}
+
+func TestDefaultReplyID_NoMatch(t *testing.T) {
+	usages := []SignatureUsage{
+		{EmailAddress: "other@example.com", ReplySignatureID: "sig-reply-other"},
+	}
+	if got := DefaultReplyID(usages, "user@example.com"); got != "" {
+		t.Fatalf("expected empty string for no match, got %q", got)
+	}
+}
+
+func TestDefaultReplyID_ZeroIDTreatedAsNone(t *testing.T) {
+	usages := []SignatureUsage{
+		{EmailAddress: "user@example.com", ReplySignatureID: "0"},
+	}
+	if got := DefaultReplyID(usages, "user@example.com"); got != "" {
+		t.Fatalf("expected empty string for ID=0, got %q", got)
+	}
+}
+
+func TestDefaultReplyID_NilUsages(t *testing.T) {
+	if got := DefaultReplyID(nil, "user@example.com"); got != "" {
+		t.Fatalf("expected empty string for nil usages, got %q", got)
+	}
+}
diff --git a/shortcuts/mail/signature_compose.go b/shortcuts/mail/signature_compose.go
index ac7f13cde..f41a1ebb8 100644
--- a/shortcuts/mail/signature_compose.go
+++ b/shortcuts/mail/signature_compose.go
@@ -5,6 +5,7 @@ package mail
 
 import (
 	"context"
+	"fmt"
 	"io"
 	"net/http"
 	"net/url"
@@ -25,6 +26,54 @@ var signatureFlag = common.Flag{
 	Desc: "Optional. Signature ID to append after body content. Run `mail +signature` to list available signatures.",
 }
 
+// noSignatureFlag is shared by all 5 compose shortcuts.
+var noSignatureFlag = common.Flag{
+	Name: "no-signature",
+	Type: "bool",
+	Desc: "Skip automatic default signature insertion. Mutually exclusive with --signature-id.",
+}
+
+// validateNoSignatureConflict returns a structured validation error when
+// --no-signature and --signature-id are both set; they are mutually exclusive.
+func validateNoSignatureConflict(noSignature bool, signatureID string) error {
+	if noSignature && signatureID != "" {
+		return mailValidationParamError("--no-signature", "--no-signature and --signature-id are mutually exclusive")
+	}
+	return nil
+}
+
+// autoResolveSignatureID resolves the default signature ID for the given mailbox/sender.
+// isReply=true uses DefaultReplyID (+reply/+reply-all/+forward);
+// isReply=false uses DefaultSendID (+send/+draft-create).
+// Returns "" on API failure (writes stderr warning) or when no default is configured.
+func autoResolveSignatureID(runtime *common.RuntimeContext, mailboxID, senderEmail string, isReply bool) string {
+	resp, err := signature.ListAll(runtime, mailboxID)
+	if err != nil {
+		fmt.Fprintf(runtime.IO().ErrOut,
+			"warning: failed to fetch default signature: %v; sending without signature\n", err)
+		return ""
+	}
+	if isReply {
+		return signature.DefaultReplyID(resp.Usages, senderEmail)
+	}
+	return signature.DefaultSendID(resp.Usages, senderEmail)
+}
+
+// injectPlainTextSignature appends a plain-text rendering of the signature to a
+// plain-text body. The HTML signature (sig.RenderedContent) is converted via
+// draftpkg.PlainTextFromHTML; inline images are dropped (plain text has none).
+// Returns textBody unchanged when sig is nil.
+func injectPlainTextSignature(textBody string, sig *signatureResult) string {
+	if sig == nil {
+		return textBody
+	}
+	sigText := strings.TrimRight(draftpkg.PlainTextFromHTML(sig.RenderedContent), "\n")
+	if sigText == "" {
+		return textBody
+	}
+	return textBody + "\n\n" + sigText
+}
+
 // signatureResult holds the pre-processed signature data ready for HTML injection.
 type signatureResult struct {
 	ID              string
@@ -32,16 +81,32 @@ type signatureResult struct {
 	Images          []draftpkg.SignatureImage
 }
 
-// resolveSignature fetches, interpolates, and downloads images for a signature.
+// resolveSignature fetches, interpolates, and optionally downloads images for a signature.
 // fromEmail is the --from address (may be an alias); used to match the correct
 // sender identity for template interpolation. Pass "" to use the primary address.
-func resolveSignature(ctx context.Context, runtime *common.RuntimeContext, mailboxID, signatureID, fromEmail string) (*signatureResult, error) {
+//
+// userExplicit must be true when the caller obtained signatureID from a user-supplied flag
+// (--signature-id); false when the ID was auto-resolved from default usages. When false,
+// a "not found" error from the signatures API is treated as graceful degradation (no
+// signature) rather than a hard failure — this protects against stale default IDs.
+//
+// includeImages controls whether inline image attachments are downloaded. Pass false for
+// plain-text compose paths to avoid unnecessary network I/O (images are discarded in
+// plain-text mode anyway).
+func resolveSignature(ctx context.Context, runtime *common.RuntimeContext, mailboxID, signatureID, fromEmail string, userExplicit, includeImages bool) (*signatureResult, error) {
 	if signatureID == "" {
 		return nil, nil
 	}
 
 	sig, err := signature.Get(runtime, mailboxID, signatureID)
 	if err != nil {
+		if !userExplicit && errs.IsValidation(err) {
+			// Stale auto-resolved default signature ID — degrade gracefully instead of
+			// blocking the entire send/reply/forward operation.
+			fmt.Fprintf(runtime.IO().ErrOut,
+				"warning: default signature %q not found in current list; sending without signature\n", signatureID)
+			return nil, nil
+		}
 		return nil, err
 	}
 
@@ -50,23 +115,26 @@ func resolveSignature(ctx context.Context, runtime *common.RuntimeContext, mailb
 	senderName, senderEmail := resolveSenderInfo(runtime, mailboxID, fromEmail)
 	rendered := signature.InterpolateTemplate(sig, lang, senderName, senderEmail)
 
-	// Download signature inline images. The file_key field contains a
-	// direct download URL provided by the mail backend.
+	// Download signature inline images only when the compose path needs them.
+	// Plain-text paths discard images, so skip the download to avoid unnecessary
+	// network I/O (and potential failures from expired pre-signed URLs).
 	var images []draftpkg.SignatureImage
-	for _, img := range sig.Images {
-		if img.DownloadURL == "" || img.CID == "" {
-			continue
+	if includeImages {
+		for _, img := range sig.Images {
+			if img.DownloadURL == "" || img.CID == "" {
+				continue
+			}
+			data, ct, err := downloadSignatureImage(runtime, img.DownloadURL, img.ImageName)
+			if err != nil {
+				return nil, mailDecorateProblemMessage(err, "failed to download signature image %s", img.ImageName)
+			}
+			images = append(images, draftpkg.SignatureImage{
+				CID:         img.CID,
+				ContentType: ct,
+				FileName:    img.ImageName,
+				Data:        data,
+			})
 		}
-		data, ct, err := downloadSignatureImage(runtime, img.DownloadURL, img.ImageName)
-		if err != nil {
-			return nil, mailDecorateProblemMessage(err, "failed to download signature image %s", img.ImageName)
-		}
-		images = append(images, draftpkg.SignatureImage{
-			CID:         img.CID,
-			ContentType: ct,
-			FileName:    img.ImageName,
-			Data:        data,
-		})
 	}
 
 	return &signatureResult{
@@ -243,15 +311,3 @@ func signatureCIDs(sig *signatureResult) []string {
 	}
 	return cids
 }
-
-// validateSignatureWithPlainText returns an error if both --plain-text and --signature-id are set.
-func validateSignatureWithPlainText(plainText bool, signatureID string) error {
-	if plainText && signatureID != "" {
-		return mailValidationError("--plain-text and --signature-id are mutually exclusive: signatures require HTML mode").
-			WithParams(
-				mailInvalidParam("--plain-text", "mutually exclusive with --signature-id"),
-				mailInvalidParam("--signature-id", "requires HTML mode"),
-			)
-	}
-	return nil
-}
diff --git a/shortcuts/mail/signature_compose_test.go b/shortcuts/mail/signature_compose_test.go
index 51bf63f97..9adf52a35 100644
--- a/shortcuts/mail/signature_compose_test.go
+++ b/shortcuts/mail/signature_compose_test.go
@@ -4,204 +4,287 @@
 package mail
 
 import (
+	"context"
 	"errors"
-	"io"
-	"net/http"
-	"net/http/httptest"
 	"strings"
 	"testing"
 
+	"github.com/spf13/cobra"
+
 	"github.com/larksuite/cli/errs"
+	"github.com/larksuite/cli/internal/cmdutil"
+	"github.com/larksuite/cli/internal/core"
+	"github.com/larksuite/cli/internal/httpmock"
+	"github.com/larksuite/cli/shortcuts/common"
+	draftpkg "github.com/larksuite/cli/shortcuts/mail/draft"
+	"github.com/larksuite/cli/shortcuts/mail/emlbuilder"
 )
 
-func TestDownloadSignatureImageRejectsInvalidURLs(t *testing.T) {
-	rt := newDownloadRuntime(t, &http.Client{})
+func TestValidateNoSignatureConflictTypedError(t *testing.T) {
+	err := validateNoSignatureConflict(true, "sig_123")
+	if err == nil {
+		t.Fatal("expected error, got nil")
+	}
+	// mailValidationParamError returns *errs.ValidationError.
+	var valErr *errs.ValidationError
+	if !errors.As(err, &valErr) {
+		t.Fatalf("expected *errs.ValidationError, got %T: %v", err, err)
+	}
+	if valErr.Param != "--no-signature" {
+		t.Errorf("expected Param \"--no-signature\", got %q", valErr.Param)
+	}
+	if !strings.Contains(err.Error(), "mutually exclusive") {
+		t.Errorf("error message = %q, want it to contain \"mutually exclusive\"", err.Error())
+	}
+}
 
+func TestValidateNoSignatureConflictNoError(t *testing.T) {
+	if err := validateNoSignatureConflict(false, "sig_123"); err != nil {
+		t.Fatalf("expected no error when noSignature=false, got %v", err)
+	}
+	if err := validateNoSignatureConflict(true, ""); err != nil {
+		t.Fatalf("expected no error when signatureID empty, got %v", err)
+	}
+}
+
+func TestInjectPlainTextSignatureNilSig(t *testing.T) {
+	body := "Hello world"
+	got := injectPlainTextSignature(body, nil)
+	if got != body {
+		t.Fatalf("expected unchanged body %q, got %q", body, got)
+	}
+}
+
+func TestInjectPlainTextSignatureEmptyHTML(t *testing.T) {
+	sig := &signatureResult{RenderedContent: "   <br>   "}
+	body := "Hello world"
+	got := injectPlainTextSignature(body, sig)
+	// PlainTextFromHTML on whitespace-only HTML collapses to empty — body unchanged.
+	if got != body {
+		t.Fatalf("expected unchanged body for empty HTML sig, got %q", got)
+	}
+}
+
+func TestInjectPlainTextSignatureAppendsWithBlankLine(t *testing.T) {
+	sig := &signatureResult{RenderedContent: "<div>Best,<br>Bob</div>"}
+	body := "Hello world"
+	got := injectPlainTextSignature(body, sig)
+	if !strings.HasPrefix(got, body+"\n\n") {
+		t.Fatalf("expected body followed by two newlines, got %q", got)
+	}
+	if !strings.Contains(got, "Best,") || !strings.Contains(got, "Bob") {
+		t.Fatalf("expected sig text in result, got %q", got)
+	}
+}
+
+func TestInjectPlainTextSignatureTrimsTrailingNewlines(t *testing.T) {
+	// RenderedContent whose plain-text rendering ends in newlines must be trimmed.
+	sig := &signatureResult{RenderedContent: "<p>Alice</p>"}
+	body := "My message"
+	got := injectPlainTextSignature(body, sig)
+	// Result must not end with a bare newline after the signature text.
+	if strings.HasSuffix(got, "\n") {
+		t.Fatalf("result should not end with newline, got %q", got)
+	}
+	if !strings.Contains(got, "Alice") {
+		t.Fatalf("expected sig text in result, got %q", got)
+	}
+}
+
+func TestContentTypeFromFilename(t *testing.T) {
 	cases := []struct {
 		name string
-		url  string
+		want string
 	}{
-		{name: "invalid", url: "https://[::1"},
-		{name: "http", url: "http://example.com/sig.png"},
-		{name: "no host", url: "https:///sig.png"},
+		{"logo.png", "image/png"},
+		{"photo.jpg", "image/jpeg"},
+		{"photo.jpeg", "image/jpeg"},
+		{"anim.gif", "image/gif"},
+		{"icon.webp", "image/webp"},
+		{"draw.svg", "image/svg+xml"},
+		{"bitmap.bmp", "image/bmp"},
+		{"data.bin", "application/octet-stream"},
+		{"noext", "application/octet-stream"},
+		{"UPPER.PNG", "image/png"},
 	}
-
 	for _, tc := range cases {
-		t.Run(tc.name, func(t *testing.T) {
-			_, _, err := downloadSignatureImage(rt, tc.url, "sig.png")
-			var internalErr *errs.InternalError
-			if !errors.As(err, &internalErr) {
-				t.Fatalf("expected internal error, got %T (%v)", err, err)
-			}
-			p, ok := errs.ProblemOf(err)
-			if !ok {
-				t.Fatalf("expected typed problem, got %T", err)
-			}
-			if p.Subtype != errs.SubtypeInvalidResponse {
-				t.Fatalf("subtype = %q, want %q", p.Subtype, errs.SubtypeInvalidResponse)
-			}
-		})
+		got := contentTypeFromFilename(tc.name)
+		if got != tc.want {
+			t.Errorf("contentTypeFromFilename(%q) = %q, want %q", tc.name, got, tc.want)
+		}
 	}
 }
 
-func TestDownloadSignatureImageHTTPErrorClassification(t *testing.T) {
-	for _, tc := range []struct {
-		name       string
-		statusCode int
-		wantType   any
-		wantSub    errs.Subtype
-		retryable  bool
-	}{
-		{
-			name:       "server",
-			statusCode: http.StatusInternalServerError,
-			wantType:   (*errs.NetworkError)(nil),
-			wantSub:    errs.SubtypeNetworkServer,
-			retryable:  true,
+func TestSignatureCIDsNilSig(t *testing.T) {
+	if cids := signatureCIDs(nil); cids != nil {
+		t.Fatalf("expected nil slice for nil sig, got %v", cids)
+	}
+}
+
+func TestSignatureCIDsFiltersEmpty(t *testing.T) {
+	sig := &signatureResult{
+		Images: []draftpkg.SignatureImage{
+			{CID: "abc123"},
+			{CID: ""},
+			{CID: "<def456>"},
 		},
-		{
-			name:       "not found",
-			statusCode: http.StatusNotFound,
-			wantType:   (*errs.APIError)(nil),
-			wantSub:    errs.SubtypeNotFound,
+	}
+	cids := signatureCIDs(sig)
+	// normalizeInlineCID strips angle brackets; empty CID is filtered out.
+	if len(cids) != 2 {
+		t.Fatalf("expected 2 CIDs, got %d: %v", len(cids), cids)
+	}
+	for _, c := range cids {
+		if c == "" {
+			t.Errorf("CID must not be empty string; got %v", cids)
+		}
+	}
+}
+
+func TestInjectSignatureIntoBodyNilSig(t *testing.T) {
+	html := "<div>body</div>"
+	got := injectSignatureIntoBody(html, nil)
+	if got != html {
+		t.Fatalf("expected unchanged body for nil sig, got %q", got)
+	}
+}
+
+func TestInjectSignatureIntoBodyInjectsSig(t *testing.T) {
+	html := "<div>Hello</div>"
+	sig := &signatureResult{
+		ID:              "sig1",
+		RenderedContent: "<div>-- Alice</div>",
+	}
+	got := injectSignatureIntoBody(html, sig)
+	if !strings.Contains(got, "sig1") && !strings.Contains(got, "Alice") {
+		t.Fatalf("expected signature content in result, got %q", got)
+	}
+}
+
+func TestAddSignatureImagesToBuilderNilSig(t *testing.T) {
+	bld := emlbuilder.New()
+	got := addSignatureImagesToBuilder(bld, nil)
+	// nil sig must return the builder unchanged (no panic, no nil return).
+	_ = got
+}
+
+func TestAddSignatureImagesToBuilderWithImages(t *testing.T) {
+	bld := emlbuilder.New()
+	sig := &signatureResult{
+		Images: []draftpkg.SignatureImage{
+			{CID: "img1", ContentType: "image/png", FileName: "logo.png", Data: []byte("fake")},
+			{CID: "", ContentType: "image/jpeg", FileName: "skip.jpg", Data: []byte("fake")}, // empty CID skipped
 		},
-	} {
-		t.Run(tc.name, func(t *testing.T) {
-			srv := httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
-				http.Error(w, "download failed", tc.statusCode)
-			}))
-			t.Cleanup(srv.Close)
-			rt := newDownloadRuntime(t, srv.Client())
+	}
+	// Should not panic; empty CID entry is silently skipped.
+	got := addSignatureImagesToBuilder(bld, sig)
+	_ = got
+}
 
-			_, _, err := downloadSignatureImage(rt, srv.URL+"/sig.png", "sig.png")
-			switch tc.wantType.(type) {
-			case *errs.NetworkError:
-				var networkErr *errs.NetworkError
-				if !errors.As(err, &networkErr) {
-					t.Fatalf("expected network error, got %T (%v)", err, err)
-				}
-			case *errs.APIError:
-				var apiErr *errs.APIError
-				if !errors.As(err, &apiErr) {
-					t.Fatalf("expected API error, got %T (%v)", err, err)
-				}
-			}
-			p, ok := errs.ProblemOf(err)
-			if !ok {
-				t.Fatalf("expected typed problem, got %T", err)
-			}
-			if p.Code != tc.statusCode {
-				t.Fatalf("code = %d, want %d", p.Code, tc.statusCode)
-			}
-			if p.Subtype != tc.wantSub {
-				t.Fatalf("subtype = %q, want %q", p.Subtype, tc.wantSub)
-			}
-			if p.Retryable != tc.retryable {
-				t.Fatalf("retryable = %v, want %v", p.Retryable, tc.retryable)
-			}
-		})
+// newSigTestRuntime creates a RuntimeContext backed by an httpmock.Registry for
+// tests that exercise signature API code paths (autoResolveSignatureID, resolveSignature).
+func newSigTestRuntime(t *testing.T) (*common.RuntimeContext, *httpmock.Registry) {
+	t.Helper()
+	cfg := &core.CliConfig{Brand: core.BrandFeishu, AppID: "cli_sigtest"}
+	f, _, _, reg := cmdutil.TestFactory(t, cfg)
+	rt := common.TestNewRuntimeContextForAPI(context.Background(), &cobra.Command{Use: "+test"}, cfg, f, core.AsUser)
+	return rt, reg
+}
+
+// stubSigListResponse registers a signatures list stub for the given mailboxID.
+func stubSigListResponse(reg *httpmock.Registry, mailboxID string, sigs []map[string]interface{}, usages []map[string]interface{}) {
+	reg.Register(&httpmock.Stub{
+		Method: "GET",
+		URL:    "/open-apis/mail/v1/user_mailboxes/" + mailboxID + "/settings/signatures",
+		Body: map[string]interface{}{
+			"code": 0,
+			"data": map[string]interface{}{
+				"signatures": sigs,
+				"usages":     usages,
+			},
+		},
+	})
+}
+
+func TestAutoResolveSignatureID_APIFailureReturnsEmpty(t *testing.T) {
+	rt, reg := newSigTestRuntime(t)
+	reg.Register(&httpmock.Stub{
+		Method: "GET",
+		URL:    "/open-apis/mail/v1/user_mailboxes/mbx-api-fail/settings/signatures",
+		Status: 500,
+		Body:   map[string]interface{}{"code": 500, "msg": "internal server error"},
+	})
+	got := autoResolveSignatureID(rt, "mbx-api-fail", "user@example.com", false)
+	if got != "" {
+		t.Fatalf("expected empty string on API failure, got %q", got)
 	}
 }
 
-func TestDownloadSignatureImageReadAndSizeErrors(t *testing.T) {
-	readErr := errors.New("socket closed")
-	rt := newDownloadRuntime(t, &http.Client{
-		Transport: signatureRoundTripper(func(req *http.Request) (*http.Response, error) {
-			return &http.Response{
-				StatusCode: http.StatusOK,
-				Header:     make(http.Header),
-				Body:       signatureErrorBody{err: readErr},
-				Request:    req,
-			}, nil
-		}),
+func TestAutoResolveSignatureID_NoDefaultConfigured(t *testing.T) {
+	rt, reg := newSigTestRuntime(t)
+	stubSigListResponse(reg, "mbx-no-default", nil, []map[string]interface{}{
+		{"email_address": "other@example.com", "send_mail_signature_id": "sig-other"},
 	})
-
-	_, _, err := downloadSignatureImage(rt, "https://example.com/sig.png", "sig.png")
-	var networkErr *errs.NetworkError
-	if !errors.As(err, &networkErr) {
-		t.Fatalf("expected network error, got %T (%v)", err, err)
-	}
-	if !errors.Is(err, readErr) {
-		t.Fatalf("read cause not preserved: %v", err)
-	}
-
-	rt = newDownloadRuntime(t, &http.Client{
-		Transport: signatureRoundTripper(func(req *http.Request) (*http.Response, error) {
-			return &http.Response{
-				StatusCode: http.StatusOK,
-				Header:     make(http.Header),
-				Body:       &bodyFileTestFile{remaining: 10*1024*1024 + 1},
-				Request:    req,
-			}, nil
-		}),
-	})
-
-	_, _, err = downloadSignatureImage(rt, "https://example.com/huge.png", "huge.png")
-	var validationErr *errs.ValidationError
-	if !errors.As(err, &validationErr) {
-		t.Fatalf("expected validation error, got %T (%v)", err, err)
-	}
-	p, ok := errs.ProblemOf(err)
-	if !ok {
-		t.Fatalf("expected typed problem, got %T", err)
-	}
-	if p.Subtype != errs.SubtypeFailedPrecondition {
-		t.Fatalf("subtype = %q, want %q", p.Subtype, errs.SubtypeFailedPrecondition)
+	got := autoResolveSignatureID(rt, "mbx-no-default", "user@example.com", false)
+	if got != "" {
+		t.Fatalf("expected empty string when no default configured for sender, got %q", got)
 	}
 }
 
-func TestDownloadSignatureImageSuccessUsesFilenameContentType(t *testing.T) {
-	rt := newDownloadRuntime(t, &http.Client{
-		Transport: signatureRoundTripper(func(req *http.Request) (*http.Response, error) {
-			return &http.Response{
-				StatusCode: http.StatusOK,
-				Header:     make(http.Header),
-				Body:       io.NopCloser(strings.NewReader("gif-data")),
-				Request:    req,
-			}, nil
-		}),
+func TestAutoResolveSignatureID_ReturnsSendID(t *testing.T) {
+	rt, reg := newSigTestRuntime(t)
+	stubSigListResponse(reg, "mbx-send-id", nil, []map[string]interface{}{
+		{"email_address": "user@example.com", "send_mail_signature_id": "sig-send-42", "reply_signature_id": "sig-reply-42"},
 	})
+	got := autoResolveSignatureID(rt, "mbx-send-id", "user@example.com", false)
+	if got != "sig-send-42" {
+		t.Fatalf("expected send default sig ID %q, got %q", "sig-send-42", got)
+	}
+}
 
-	data, contentType, err := downloadSignatureImage(rt, "https://example.com/sig.gif", "sig.gif")
+func TestAutoResolveSignatureID_ReturnsReplyID(t *testing.T) {
+	rt, reg := newSigTestRuntime(t)
+	stubSigListResponse(reg, "mbx-reply-id", nil, []map[string]interface{}{
+		{"email_address": "user@example.com", "send_mail_signature_id": "sig-send-42", "reply_signature_id": "sig-reply-42"},
+	})
+	got := autoResolveSignatureID(rt, "mbx-reply-id", "user@example.com", true)
+	if got != "sig-reply-42" {
+		t.Fatalf("expected reply default sig ID %q, got %q", "sig-reply-42", got)
+	}
+}
+
+func TestResolveSignature_EmptyIDReturnsNil(t *testing.T) {
+	rt, _ := newSigTestRuntime(t)
+	result, err := resolveSignature(context.Background(), rt, "mbx-empty", "", "user@example.com", false, false)
 	if err != nil {
-		t.Fatalf("downloadSignatureImage failed: %v", err)
+		t.Fatalf("unexpected error for empty signatureID: %v", err)
 	}
-	if string(data) != "gif-data" {
-		t.Fatalf("data = %q", string(data))
-	}
-	if contentType != "image/gif" {
-		t.Fatalf("content type = %q, want image/gif", contentType)
+	if result != nil {
+		t.Fatalf("expected nil result for empty signatureID, got %+v", result)
 	}
 }
 
-func TestValidateSignatureWithPlainTextTypedError(t *testing.T) {
-	err := validateSignatureWithPlainText(true, "sig_123")
-	var validationErr *errs.ValidationError
-	if !errors.As(err, &validationErr) {
-		t.Fatalf("expected validation error, got %T (%v)", err, err)
+func TestResolveSignature_StaleIDAutoDegradesGracefully(t *testing.T) {
+	rt, reg := newSigTestRuntime(t)
+	// API returns an empty list — stale ID not found → ValidationError in Get.
+	stubSigListResponse(reg, "mbx-stale-auto", nil, nil)
+	result, err := resolveSignature(context.Background(), rt, "mbx-stale-auto", "sig-stale", "user@example.com", false, false)
+	if err != nil {
+		t.Fatalf("expected graceful degradation (nil error), got: %v", err)
 	}
-	if len(validationErr.Params) != 2 {
-		t.Fatalf("params = %#v, want two conflicting params", validationErr.Params)
-	}
-	if validationErr.Params[0].Name != "--plain-text" || validationErr.Params[1].Name != "--signature-id" {
-		t.Fatalf("unexpected params: %#v", validationErr.Params)
+	if result != nil {
+		t.Fatalf("expected nil result for stale auto-resolved ID, got %+v", result)
 	}
 }
 
-type signatureRoundTripper func(*http.Request) (*http.Response, error)
-
-func (rt signatureRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
-	return rt(req)
-}
-
-type signatureErrorBody struct {
-	err error
-}
-
-func (b signatureErrorBody) Read([]byte) (int, error) {
-	return 0, b.err
-}
-
-func (b signatureErrorBody) Close() error {
-	return nil
+func TestResolveSignature_StaleIDUserExplicitFails(t *testing.T) {
+	rt, reg := newSigTestRuntime(t)
+	stubSigListResponse(reg, "mbx-stale-explicit", nil, nil)
+	_, err := resolveSignature(context.Background(), rt, "mbx-stale-explicit", "sig-stale", "user@example.com", true, false)
+	if err == nil {
+		t.Fatal("expected error for stale ID with userExplicit=true, got nil")
+	}
+	if !errs.IsValidation(err) {
+		t.Fatalf("expected validation error, got %T: %v", err, err)
+	}
 }
diff --git a/skills/lark-mail/references/lark-mail-draft-create.md b/skills/lark-mail/references/lark-mail-draft-create.md
index 36b6682dd..e0fe3cb37 100644
--- a/skills/lark-mail/references/lark-mail-draft-create.md
+++ b/skills/lark-mail/references/lark-mail-draft-create.md
@@ -52,10 +52,11 @@ lark-cli mail +draft-create --to alice@example.com --subject '测试' --body 'te
 | `--mailbox <email>` | 否 | 邮箱地址，指定草稿所属的邮箱（默认回退到 `--from`，再回退到 `me`）。当发件人（`--from`）与邮箱不同时使用，如通过别名或 send_as 地址发信。可通过 `accessible_mailboxes` 查询可用邮箱 |
 | `--cc <emails>` | 否 | 完整抄送列表，多个用逗号分隔 |
 | `--bcc <emails>` | 否 | 完整密送列表，多个用逗号分隔。与 `--event-*` 不兼容（见 `+send` 日程邀请约束） |
-| `--plain-text` | 否 | 强制纯文本模式，忽略 HTML 自动检测。不可与 `--inline` 同时使用 |
+| `--plain-text` | 否 | 强制纯文本模式，忽略 HTML 自动检测。不可与 `--inline` 同时使用。纯文本模式下也会自动追加纯文本签名（HTML 签名经 `PlainTextFromHTML` 转换，内联图片丢弃） |
 | `--attach <paths>` | 否 | 附件文件路径，多个用逗号分隔。相对路径。当附件导致 EML 总大小超过 25 MB 时，超出部分自动上传为超大附件（HTML 邮件插入下载卡片，纯文本邮件追加下载链接），单个文件上限 3 GB |
 | `--inline <json>` | 否 | 高级用法：手动指定内嵌图片 CID 映射。推荐直接在 `--body` 中使用 `<img src="./path" />`（自动解析）。仅在需要精确控制 CID 命名时使用此参数。格式：`'[{"cid":"mycid","file_path":"./logo.png"}]'`，在 body 中用 `<img src="cid:mycid">` 引用。不可与 `--plain-text` 同时使用 |
-| `--signature-id <id>` | 否 | 签名 ID。附加邮箱签名到正文末尾。运行 `mail +signature` 查看可用签名。不可与 `--plain-text` 同时使用 |
+| `--signature-id <id>` | 否 | 签名 ID。附加邮箱签名到正文末尾。运行 `mail +signature` 查看可用签名。与 `--no-signature` 互斥 |
+| `--no-signature` | 否 | 跳过默认签名自动追加。与 `--signature-id` 互斥，同时使用时返回参数校验错误（退出码 2） |
 | `--priority <level>` | 否 | 邮件优先级：`high`、`normal`、`low`。省略或 `normal` 时不设置优先级 |
 | `--request-receipt` | 否 | 请求已读回执（RFC 3798 Message Disposition Notification）。在草稿 EML 里写 `Disposition-Notification-To: <sender>` 头，发送时生效。收件人的邮件客户端可能弹出提示、自动发送或忽略——送达不保证 |
 | `--event-summary <text>` | 否 | 日程标题。设置此参数即在邮件中嵌入日程邀请。需同时设置 `--event-start` 和 `--event-end` |
diff --git a/skills/lark-mail/references/lark-mail-forward.md b/skills/lark-mail/references/lark-mail-forward.md
index 9545161cd..3597ef74a 100644
--- a/skills/lark-mail/references/lark-mail-forward.md
+++ b/skills/lark-mail/references/lark-mail-forward.md
@@ -68,10 +68,11 @@ lark-cli mail +forward --message-id <邮件ID> --to alice@example.com --dry-run
 | `--mailbox <email>` | 否 | 邮箱地址，指定草稿所属的邮箱（默认回退到 `--from`，再回退到 `me`）。当发件人（`--from`）与邮箱不同时使用。可通过 `accessible_mailboxes` 查询可用邮箱 |
 | `--cc <emails>` | 否 | 抄送邮箱，多个用逗号分隔 |
 | `--bcc <emails>` | 否 | 密送邮箱，多个用逗号分隔。与 `--event-*` 不兼容（见 `+send` 日程邀请约束） |
-| `--plain-text` | 否 | 强制纯文本模式，忽略所有 HTML 自动检测。不可与 `--inline` 同时使用 |
+| `--plain-text` | 否 | 强制纯文本模式，忽略所有 HTML 自动检测。不可与 `--inline` 同时使用。纯文本模式下也会自动追加纯文本签名（HTML 签名经 `PlainTextFromHTML` 转换，内联图片丢弃） |
 | `--attach <paths>` | 否 | 附件文件路径，多个用逗号分隔，追加在原邮件附件之后。相对路径。当附件导致 EML 总大小超过 25 MB 时，超出部分自动上传为超大附件（HTML 邮件插入下载卡片，纯文本邮件追加下载链接），单个文件上限 3 GB |
 | `--inline <json>` | 否 | 高级用法：手动指定内嵌图片 CID 映射。推荐直接在 `--body` 中使用 `<img src="./path" />`（自动解析）。仅在需要精确控制 CID 命名时使用此参数。格式：`'[{"cid":"mycid","file_path":"./logo.png"}]'`，在 body 中用 `<img src="cid:mycid">` 引用。不可与 `--plain-text` 同时使用 |
-| `--signature-id <id>` | 否 | 签名 ID。附加邮箱签名到转发正文与引用块之间。运行 `mail +signature` 查看可用签名。不可与 `--plain-text` 同时使用 |
+| `--signature-id <id>` | 否 | 签名 ID。附加邮箱签名到转发正文与引用块之间。运行 `mail +signature` 查看可用签名。与 `--no-signature` 互斥 |
+| `--no-signature` | 否 | 跳过默认签名自动追加。与 `--signature-id` 互斥，同时使用时返回参数校验错误（退出码 2） |
 | `--priority <level>` | 否 | 邮件优先级：`high`、`normal`、`low`。省略或 `normal` 时不设置优先级 |
 | `--event-summary <text>` | 否 | 日程标题。设置此参数即在邮件中嵌入日程邀请。需同时设置 `--event-start` 和 `--event-end` |
 | `--event-start <time>` | 条件必填 | 日程开始时间（ISO 8601） |
diff --git a/skills/lark-mail/references/lark-mail-reply-all.md b/skills/lark-mail/references/lark-mail-reply-all.md
index 76dbc0812..9682981f8 100644
--- a/skills/lark-mail/references/lark-mail-reply-all.md
+++ b/skills/lark-mail/references/lark-mail-reply-all.md
@@ -72,10 +72,11 @@ lark-cli mail +reply-all --message-id <邮件ID> --body '测试' --dry-run
 | `--cc <emails>` | 否 | 额外抄送，多个用逗号分隔 |
 | `--bcc <emails>` | 否 | 密送邮箱，多个用逗号分隔。与 `--event-*` 不兼容（见 `+send` 日程邀请约束） |
 | `--remove <emails>` | 否 | 从自动聚合结果中排除的邮箱，多个用逗号分隔 |
-| `--plain-text` | 否 | 强制纯文本模式，忽略所有 HTML 自动检测。不可与 `--inline` 同时使用 |
+| `--plain-text` | 否 | 强制纯文本模式，忽略所有 HTML 自动检测。不可与 `--inline` 同时使用。纯文本模式下也会自动追加纯文本签名（HTML 签名经 `PlainTextFromHTML` 转换，内联图片丢弃） |
 | `--attach <paths>` | 否 | 附件文件路径，多个用逗号分隔。相对路径。当附件导致 EML 总大小超过 25 MB 时，超出部分自动上传为超大附件（HTML 邮件插入下载卡片，纯文本邮件追加下载链接），单个文件上限 3 GB |
 | `--inline <json>` | 否 | 高级用法：手动指定内嵌图片 CID 映射。推荐直接在 `--body` 中使用 `<img src="./path" />`（自动解析）。仅在需要精确控制 CID 命名时使用此参数。格式：`'[{"cid":"mycid","file_path":"./logo.png"}]'`，在 body 中用 `<img src="cid:mycid">` 引用。不可与 `--plain-text` 同时使用 |
-| `--signature-id <id>` | 否 | 签名 ID。附加邮箱签名到回复正文与引用块之间。运行 `mail +signature` 查看可用签名。不可与 `--plain-text` 同时使用 |
+| `--signature-id <id>` | 否 | 签名 ID。附加邮箱签名到回复正文与引用块之间。运行 `mail +signature` 查看可用签名。与 `--no-signature` 互斥 |
+| `--no-signature` | 否 | 跳过默认签名自动追加。与 `--signature-id` 互斥，同时使用时返回参数校验错误（退出码 2） |
 | `--priority <level>` | 否 | 邮件优先级：`high`、`normal`、`low`。省略或 `normal` 时不设置优先级 |
 | `--event-summary <text>` | 否 | 日程标题。设置此参数即在邮件中嵌入日程邀请。需同时设置 `--event-start` 和 `--event-end` |
 | `--event-start <time>` | 条件必填 | 日程开始时间（ISO 8601） |
diff --git a/skills/lark-mail/references/lark-mail-reply.md b/skills/lark-mail/references/lark-mail-reply.md
index ba6be3762..8b5fd7c8e 100644
--- a/skills/lark-mail/references/lark-mail-reply.md
+++ b/skills/lark-mail/references/lark-mail-reply.md
@@ -75,10 +75,11 @@ lark-cli mail +reply --message-id <邮件ID> --body '<p>测试</p>' --dry-run
 | `--to <emails>` | 否 | 额外收件人，多个用逗号分隔（追加到原发件人） |
 | `--cc <emails>` | 否 | 抄送邮箱，多个用逗号分隔 |
 | `--bcc <emails>` | 否 | 密送邮箱，多个用逗号分隔。与 `--event-*` 不兼容（见 `+send` 日程邀请约束） |
-| `--plain-text` | 否 | 强制纯文本模式，忽略所有 HTML 自动检测。不可与 `--inline` 同时使用 |
+| `--plain-text` | 否 | 强制纯文本模式，忽略所有 HTML 自动检测。不可与 `--inline` 同时使用。纯文本模式下也会自动追加纯文本签名（HTML 签名经 `PlainTextFromHTML` 转换，内联图片丢弃） |
 | `--attach <paths>` | 否 | 附件文件路径，多个用逗号分隔。相对路径。当附件导致 EML 总大小超过 25 MB 时，超出部分自动上传为超大附件（HTML 邮件插入下载卡片，纯文本邮件追加下载链接），单个文件上限 3 GB |
 | `--inline <json>` | 否 | 高级用法：手动指定内嵌图片 CID 映射。推荐直接在 `--body` 中使用 `<img src="./path" />`（自动解析）。仅在需要精确控制 CID 命名时使用此参数。格式：`'[{"cid":"mycid","file_path":"./logo.png"}]'`，在 body 中用 `<img src="cid:mycid">` 引用。不可与 `--plain-text` 同时使用 |
-| `--signature-id <id>` | 否 | 签名 ID。附加邮箱签名到回复正文与引用块之间。运行 `mail +signature` 查看可用签名。不可与 `--plain-text` 同时使用 |
+| `--signature-id <id>` | 否 | 签名 ID。附加邮箱签名到回复正文与引用块之间。运行 `mail +signature` 查看可用签名。与 `--no-signature` 互斥 |
+| `--no-signature` | 否 | 跳过默认签名自动追加。与 `--signature-id` 互斥，同时使用时返回参数校验错误（退出码 2） |
 | `--priority <level>` | 否 | 邮件优先级：`high`、`normal`、`low`。省略或 `normal` 时不设置优先级 |
 | `--event-summary <text>` | 否 | 日程标题。设置此参数即在邮件中嵌入日程邀请。需同时设置 `--event-start` 和 `--event-end` |
 | `--event-start <time>` | 条件必填 | 日程开始时间（ISO 8601） |
diff --git a/skills/lark-mail/references/lark-mail-send.md b/skills/lark-mail/references/lark-mail-send.md
index 500feca41..212135aeb 100644
--- a/skills/lark-mail/references/lark-mail-send.md
+++ b/skills/lark-mail/references/lark-mail-send.md
@@ -75,10 +75,11 @@ lark-cli mail +send --to alice@example.com --subject '测试' --body '<p>test</p
 | `--mailbox <email>` | 否 | 邮箱地址，指定草稿所属的邮箱（默认回退到 `--from`，再回退到 `me`）。当发件人（`--from`）与邮箱不同时使用。可通过 `accessible_mailboxes` 查询可用邮箱 |
 | `--cc <emails>` | 否 | 抄送邮箱，多个用逗号分隔 |
 | `--bcc <emails>` | 否 | 密送邮箱，多个用逗号分隔 |
-| `--plain-text` | 否 | 强制纯文本模式，忽略 HTML 自动检测。不可与 `--inline` 同时使用 |
+| `--plain-text` | 否 | 强制纯文本模式，忽略 HTML 自动检测。不可与 `--inline` 同时使用。纯文本模式下也会自动追加纯文本签名（HTML 签名经 `PlainTextFromHTML` 转换，内联图片丢弃） |
 | `--attach <paths>` | 否 | 附件文件路径，多个用逗号分隔。相对路径。当附件导致 EML 总大小超过 25 MB 时，超出部分自动上传为超大附件（HTML 邮件插入下载卡片，纯文本邮件追加下载链接），单个文件上限 3 GB |
 | `--inline <json>` | 否 | 高级用法：手动指定内嵌图片 CID 映射。推荐直接在 `--body` 中使用 `<img src="./path" />`（自动解析）。仅在需要精确控制 CID 命名时使用此参数。格式：`'[{"cid":"mycid","file_path":"./logo.png"}]'`，在 body 中用 `<img src="cid:mycid">` 引用。不可与 `--plain-text` 同时使用 |
-| `--signature-id <id>` | 否 | 签名 ID。附加邮箱签名到正文末尾。运行 `mail +signature` 查看可用签名。不可与 `--plain-text` 同时使用 |
+| `--signature-id <id>` | 否 | 签名 ID。附加邮箱签名到正文末尾。运行 `mail +signature` 查看可用签名。与 `--no-signature` 互斥 |
+| `--no-signature` | 否 | 跳过默认签名自动追加。与 `--signature-id` 互斥，同时使用时返回参数校验错误（退出码 2） |
 | `--priority <level>` | 否 | 邮件优先级：`high`、`normal`、`low`。省略或 `normal` 时不设置优先级 |
 | `--event-summary <text>` | 否 | 日程标题。设置此参数即在邮件中嵌入日程邀请（text/calendar）。需同时设置 `--event-start` 和 `--event-end` |
 | `--event-start <time>` | 条件必填 | 日程开始时间（ISO 8601，如 `2026-04-20T14:00+08:00`） |