diff --git a/app/(main)/[locale]/page.tsx b/app/(main)/[locale]/page.tsx
index 5f03ea1d7..ad703c93e 100644
--- a/app/(main)/[locale]/page.tsx
+++ b/app/(main)/[locale]/page.tsx
@@ -73,7 +73,7 @@ import { usePluginStore } from "@/stores/plugin-store";
 import { AppTopBannerSlot } from "@/components/plugins/app-top-banner-slot";
 import { useThemeStore } from "@/stores/theme-store";
 import { consumePendingMailto, subscribeToPendingMailto } from "@/lib/protocol-handlers/session";
-import type { ParsedMailto } from "@/lib/protocol-handlers/mailto";
+import { INTERNAL_MAILTO_EVENT, type ParsedMailto } from "@/lib/protocol-handlers/mailto";
 import { plainTextToComposerBody, getQuoteBodies } from "@/lib/email-composer-utils";
 import { appLifecycleHooks, uiHooks, routerHooks, toastHooks, emailHooks } from "@/lib/plugin-hooks";
 import { emailToReadView } from "@/lib/plugin-projection";
@@ -958,6 +958,25 @@ export default function Home() {
     return subscribeToPendingMailto(openPendingMailto);
   }, [isAuthenticated, client, handleMailtoProtocolRequest]);
 
+  // Address links in the app's own chrome (contact cards, sidebars, contact
+  // details) compose in place. Unlike a request arriving from the OS handler,
+  // an in-app click carries its own context - the account being read - so this
+  // goes straight to the composer instead of through the account picker.
+  // Cancelling the event tells the link its click was taken.
+  useEffect(() => {
+    if (!isAuthenticated || !client) return;
+
+    const onInternalMailto = (event: Event) => {
+      const pending = (event as CustomEvent<ParsedMailto>).detail;
+      if (!pending) return;
+      event.preventDefault();
+      openMailtoDraft(pending);
+    };
+
+    window.addEventListener(INTERNAL_MAILTO_EVENT, onInternalMailto);
+    return () => window.removeEventListener(INTERNAL_MAILTO_EVENT, onInternalMailto);
+  }, [isAuthenticated, client, openMailtoDraft]);
+
   // Fallback fetch for paths that didn't go through login()'s prefetch
   // (notably checkAuth on page refresh). Settings pages can also prefill
   // mailboxes without emails, so bootstrap emails once per client when the
diff --git a/components/contacts/contact-detail.tsx b/components/contacts/contact-detail.tsx
index 1b07d86e2..b520c23c3 100644
--- a/components/contacts/contact-detail.tsx
+++ b/components/contacts/contact-detail.tsx
@@ -4,6 +4,7 @@ import { useState, useEffect, useRef } from "react";
 import { useTranslations } from "next-intl";
 import { Mail, Phone, Building, MapPin, StickyNote, Pencil, Trash2, BookUser, Copy, Send, Globe, Cake, KeyRound, Users, Briefcase, Heart, Languages, Calendar, UserCircle, Download, MoreHorizontal, Printer } from "lucide-react";
 import { Avatar } from "@/components/ui/avatar";
+import { MailtoLink } from "@/components/ui/mailto-link";
 import { Button } from "@/components/ui/button";
 import { cn } from "@/lib/utils";
 import type { ContactCard, AnniversaryDate, PartialDate } from "@/lib/jmap/types";
@@ -232,18 +233,18 @@ export function ContactDetail({ contact, onEdit, onDelete, onAddToGroup, onDupli
               {emails.map((e, i) => (
                 <FieldRow key={`em${i}`} icon={Mail} label={e.label || formatContexts(e.contexts) || t("detail.email_default_label")}>
                   <div className="flex items-center gap-2 group">
-                    <a href={`mailto:${e.address}`} className="text-sm text-primary hover:underline break-all">
+                    <MailtoLink to={e.address} className="text-sm text-primary hover:underline break-all">
                       {e.address}
-                    </a>
+                    </MailtoLink>
                     <RowActions>
-                      <a
-                        href={`mailto:${e.address}`}
+                      <MailtoLink
+                        to={e.address}
                         className="p-1.5 rounded hover:bg-muted transition-colors touch-manipulation"
                         title={t("detail.compose_email")}
                         aria-label={t("detail.compose_email")}
                       >
                         <Send className="w-3.5 h-3.5 text-muted-foreground" />
-                      </a>
+                      </MailtoLink>
                       <CopyButton value={e.address} label={t("detail.copy_email")} successMsg={t("detail.copied")} failMsg={t("detail.copy_failed")} />
                     </RowActions>
                   </div>
diff --git a/components/email/email-viewer.tsx b/components/email/email-viewer.tsx
index bbdc0a76b..4b3c3d1c7 100644
--- a/components/email/email-viewer.tsx
+++ b/components/email/email-viewer.tsx
@@ -97,6 +97,7 @@ import { useTour } from "@/components/tour/tour-provider";
 import { useIsEmbedded } from "@/hooks/use-is-embedded";
 import { findCalendarAttachment, isCalendarMimeType } from "@/lib/calendar-invitation";
 import { RecipientPopover } from "./recipient-popover";
+import { MailtoLink } from "@/components/ui/mailto-link";
 import { isFilePreviewable, isMimeTypeSafeForInlinePreview } from "@/lib/file-preview";
 import { parseTnef, isTnefAttachment } from "@/lib/tnef";
 import { debug } from "@/lib/debug";
@@ -419,14 +420,14 @@ export function ContactSidebarPanel({
 
         {/* Quick actions */}
         <div className="px-4 pb-4 flex items-center justify-center gap-2">
-          <a
-            href={`mailto:${primaryEmail}`}
+          <MailtoLink
+            to={primaryEmail}
             className="flex items-center gap-1.5 text-xs font-medium text-muted-foreground hover:text-foreground px-3 py-2 rounded-md hover:bg-muted transition-colors border border-border"
             title={t('contact_sidebar.action_email_title')}
           >
             <Send className="w-3.5 h-3.5" />
             {t('contact_sidebar.action_email')}
-          </a>
+          </MailtoLink>
           <button
             onClick={() => handleCopy(primaryEmail)}
             className="flex items-center gap-1.5 text-xs font-medium text-muted-foreground hover:text-foreground px-3 py-2 rounded-md hover:bg-muted transition-colors border border-border"
@@ -455,9 +456,9 @@ export function ContactSidebarPanel({
               <SidebarSection icon={Mail} title={t('contact_sidebar.section_emails')}>
                 {emails.map((e, i) => (
                   <div key={i} className="flex items-center gap-2 group">
-                    <a href={`mailto:${e.address}`} className="text-sm text-primary hover:underline truncate">
+                    <MailtoLink to={e.address} className="text-sm text-primary hover:underline truncate">
                       {e.address}
-                    </a>
+                    </MailtoLink>
                     <button
                       onClick={() => handleCopy(e.address)}
                       className="p-1 rounded hover:bg-muted transition-colors opacity-0 group-hover:opacity-100 shrink-0"
diff --git a/components/email/recipient-popover.tsx b/components/email/recipient-popover.tsx
index 32b39b395..9d8029ea1 100644
--- a/components/email/recipient-popover.tsx
+++ b/components/email/recipient-popover.tsx
@@ -5,6 +5,7 @@ import { createPortal } from "react-dom";
 import { Mail, Phone, Building, ExternalLink, Copy, Send, UserPlus } from "lucide-react";
 import { Avatar } from "@/components/ui/avatar";
 import { cn } from "@/lib/utils";
+import { MailtoLink } from "@/components/ui/mailto-link";
 import { useContactStore, getContactDisplayName } from "@/stores/contact-store";
 import { toast } from "@/stores/toast-store";
 import type { ContactCard } from "@/lib/jmap/types";
@@ -210,14 +211,14 @@ export function RecipientPopover({ name, email, displayLabel, onViewContact, cla
                 <Copy className="w-3.5 h-3.5" />
                 Copy
               </button>
-              <a
-                href={`mailto:${email}`}
+              <MailtoLink
+                to={email}
                 className="flex items-center gap-1.5 text-xs text-muted-foreground hover:text-foreground px-2 py-1.5 rounded hover:bg-muted transition-colors"
                 title="Send email"
               >
                 <Send className="w-3.5 h-3.5" />
                 Email
-              </a>
+              </MailtoLink>
               {onViewContact && (
                 <button
                   onClick={handleViewContact}
diff --git a/components/ui/__tests__/mailto-link.test.tsx b/components/ui/__tests__/mailto-link.test.tsx
new file mode 100644
index 000000000..ba8bbfad3
--- /dev/null
+++ b/components/ui/__tests__/mailto-link.test.tsx
@@ -0,0 +1,89 @@
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import { render, screen, cleanup, fireEvent } from '@testing-library/react';
+import { MailtoLink } from '../mailto-link';
+import { INTERNAL_MAILTO_EVENT } from '@/lib/protocol-handlers/mailto';
+import type { ParsedMailto } from '@/lib/protocol-handlers/mailto';
+
+/**
+ * Address links in the app's own chrome must compose in place: handing a
+ * mailto: URL to the OS mail handler goes nowhere in a webmail client. The
+ * element stays an anchor with a real href so "Copy email address", middle
+ * click and assistive technology keep working - only the plain click is
+ * redirected, and only when a listener actually takes it.
+ */
+
+function listenAndHandle(): { seen: ParsedMailto[] } {
+  const seen: ParsedMailto[] = [];
+  const handler = (event: Event) => {
+    seen.push((event as CustomEvent<ParsedMailto>).detail);
+    event.preventDefault();
+  };
+  window.addEventListener(INTERNAL_MAILTO_EVENT, handler);
+  listeners.push(() => window.removeEventListener(INTERNAL_MAILTO_EVENT, handler));
+  return { seen };
+}
+
+let listeners: Array<() => void> = [];
+
+describe('MailtoLink', () => {
+  beforeEach(() => {
+    listeners = [];
+  });
+
+  afterEach(() => {
+    listeners.forEach((off) => off());
+    cleanup();
+  });
+
+  it('keeps a real mailto href so copy/middle-click still work', () => {
+    render(<MailtoLink to="ada@example.com">Email</MailtoLink>);
+    expect(screen.getByRole('link')).toHaveAttribute('href', 'mailto:ada@example.com');
+  });
+
+  it('requests the internal composer instead of the OS handler', async () => {
+    const { seen } = listenAndHandle();
+    render(<MailtoLink to="ada@example.com">Email</MailtoLink>);
+
+    const link = screen.getByRole('link');
+    const click = new MouseEvent('click', { bubbles: true, cancelable: true, button: 0 });
+    link.dispatchEvent(click);
+
+    expect(seen).toHaveLength(1);
+    expect(seen[0].to).toEqual(['ada@example.com']);
+    // Default prevented => the browser does not follow the mailto: URL.
+    expect(click.defaultPrevented).toBe(true);
+  });
+
+  it('passes subject and cc through when given a full mailto URL', () => {
+    const { seen } = listenAndHandle();
+    render(<MailtoLink to="mailto:ada@example.com?subject=Hi&cc=bob@example.com">Email</MailtoLink>);
+
+    screen.getByRole('link').dispatchEvent(
+      new MouseEvent('click', { bubbles: true, cancelable: true, button: 0 }),
+    );
+
+    expect(seen[0].subject).toBe('Hi');
+    expect(seen[0].cc).toEqual(['bob@example.com']);
+  });
+
+  it('leaves the click alone when no listener takes it', () => {
+    render(<MailtoLink to="ada@example.com">Email</MailtoLink>);
+
+    const click = new MouseEvent('click', { bubbles: true, cancelable: true, button: 0 });
+    screen.getByRole('link').dispatchEvent(click);
+
+    // Nothing handled it - fall back to the browser rather than swallowing.
+    expect(click.defaultPrevented).toBe(false);
+  });
+
+  it('leaves modified clicks to the browser', () => {
+    const { seen } = listenAndHandle();
+    render(<MailtoLink to="ada@example.com">Email</MailtoLink>);
+
+    // Ctrl-click / middle click are the user's own "open elsewhere" gestures.
+    fireEvent.click(screen.getByRole('link'), { ctrlKey: true });
+    fireEvent.click(screen.getByRole('link'), { button: 1 });
+
+    expect(seen).toHaveLength(0);
+  });
+});
diff --git a/components/ui/mailto-link.tsx b/components/ui/mailto-link.tsx
new file mode 100644
index 000000000..674c0679a
--- /dev/null
+++ b/components/ui/mailto-link.tsx
@@ -0,0 +1,41 @@
+"use client";
+
+import type { AnchorHTMLAttributes, MouseEvent, ReactNode } from "react";
+import { requestInternalMailto } from "@/lib/protocol-handlers/mailto";
+
+interface MailtoLinkProps extends Omit<AnchorHTMLAttributes<HTMLAnchorElement>, "href" | "onClick"> {
+  /** Bare address, or a full mailto: URL when subject/body are needed. */
+  to: string;
+  children: ReactNode;
+}
+
+/**
+ * An address in the app's own chrome (contact cards, sidebars, contact
+ * details). Handing a `mailto:` URL to the OS mail handler goes nowhere in a
+ * webmail client - unless the user happened to register Bulwark as their
+ * system handler - so the click opens the built-in composer instead.
+ *
+ * Deliberately still an anchor with a real href: right-click "Copy email
+ * address", middle-click and assistive technology all keep working, and a
+ * plain click is simply redirected. Modified clicks are left alone.
+ *
+ * Only for app chrome. Links inside message content are untrusted and keep
+ * their existing behaviour.
+ */
+export function MailtoLink({ to, children, ...anchorProps }: MailtoLinkProps) {
+  const href = to.toLowerCase().startsWith("mailto:") ? to : `mailto:${to}`;
+
+  const handleClick = (event: MouseEvent<HTMLAnchorElement>) => {
+    // Let the browser handle "open in new tab/window" style clicks.
+    if (event.defaultPrevented || event.button !== 0) return;
+    if (event.metaKey || event.ctrlKey || event.shiftKey || event.altKey) return;
+    if (!requestInternalMailto(href)) return;
+    event.preventDefault();
+  };
+
+  return (
+    <a href={href} onClick={handleClick} {...anchorProps}>
+      {children}
+    </a>
+  );
+}
diff --git a/lib/protocol-handlers/mailto.ts b/lib/protocol-handlers/mailto.ts
index c05c79ce0..765bd6040 100644
--- a/lib/protocol-handlers/mailto.ts
+++ b/lib/protocol-handlers/mailto.ts
@@ -116,3 +116,28 @@ export function parseMailto(raw: string): ParsedMailto | null {
     body: stripBodyControlChars(getQueryValue(searchParams, "body")).slice(0, MAX_BODY_LENGTH),
   };
 }
+
+/** Window event carrying a parsed in-app mailto request to the mail page. */
+export const INTERNAL_MAILTO_EVENT = "bulwark:mailto";
+
+/**
+ * Ask the mail page to open its composer for an in-app `mailto:` click.
+ * Loosely coupled through a window event (as `bulwark:rate-limit-blocked`
+ * already is) because the composer state lives in the page component, several
+ * levels above the address links in cards and sidebars.
+ *
+ * Returns whether the request was taken: false when the URL is unusable or no
+ * listener is mounted, so callers can fall back to the browser's behaviour
+ * rather than swallowing the click.
+ */
+export function requestInternalMailto(raw: string): boolean {
+  if (typeof window === "undefined") return false;
+  const parsed = parseMailto(raw);
+  if (!parsed || parsed.to.length === 0) return false;
+  // The listener signals "handled" by cancelling the event, which makes
+  // dispatchEvent report false - so an uncancelled dispatch means nobody took it.
+  const uncancelled = window.dispatchEvent(
+    new CustomEvent<ParsedMailto>(INTERNAL_MAILTO_EVENT, { detail: parsed, cancelable: true }),
+  );
+  return !uncancelled;
+}