diff --git a/app/admin/layout.tsx b/app/admin/layout.tsx
index 5ff8e6dd..8d52db75 100644
--- a/app/admin/layout.tsx
+++ b/app/admin/layout.tsx
@@ -14,6 +14,11 @@ import {
   KeyRound,
   Puzzle,
   SwatchBook,
+  Mail,
+  Calendar,
+  BookUser,
+  HardDrive,
+  ArrowLeft,
 } from 'lucide-react';
 import { cn } from '@/lib/utils';
 import { useConfig } from '@/hooks/use-config';
@@ -139,7 +144,56 @@ export default function AdminLayout({ children }: { children: React.ReactNode })
 
   return (
     <div className="min-h-screen flex bg-background">
-      {/* Sidebar */}
+      {/* Slim webmail nav rail */}
+      <nav className="w-14 bg-secondary flex flex-col items-center py-3 gap-2 border-r border-border sticky top-0 h-screen shrink-0">
+        {logoUrl ? (
+          <img src={logoUrl} alt="" className="w-7 h-7 object-contain mb-2" />
+        ) : (
+          <div className="w-7 h-7 mb-2" />
+        )}
+        <a
+          href="/"
+          className="flex items-center justify-center w-10 h-10 rounded-md transition-colors text-muted-foreground hover:text-foreground hover:bg-muted"
+          title="Mail"
+        >
+          <Mail className="w-[18px] h-[18px]" />
+        </a>
+        <a
+          href="/calendar"
+          className="flex items-center justify-center w-10 h-10 rounded-md transition-colors text-muted-foreground hover:text-foreground hover:bg-muted"
+          title="Calendar"
+        >
+          <Calendar className="w-[18px] h-[18px]" />
+        </a>
+        <a
+          href="/contacts"
+          className="flex items-center justify-center w-10 h-10 rounded-md transition-colors text-muted-foreground hover:text-foreground hover:bg-muted"
+          title="Contacts"
+        >
+          <BookUser className="w-[18px] h-[18px]" />
+        </a>
+        <a
+          href="/files"
+          className="flex items-center justify-center w-10 h-10 rounded-md transition-colors text-muted-foreground hover:text-foreground hover:bg-muted"
+          title="Files"
+        >
+          <HardDrive className="w-[18px] h-[18px]" />
+        </a>
+        <div className="mt-auto flex flex-col items-center gap-2">
+          <div className="flex items-center justify-center w-10 h-10 rounded-md bg-primary/10 text-primary" title="Admin">
+            <Shield className="w-[18px] h-[18px]" />
+          </div>
+          <a
+            href="/settings"
+            className="flex items-center justify-center w-10 h-10 rounded-md transition-colors text-muted-foreground hover:text-foreground hover:bg-muted"
+            title="Settings"
+          >
+            <Settings className="w-[18px] h-[18px]" />
+          </a>
+        </div>
+      </nav>
+
+      {/* Admin Sidebar */}
       <aside className="w-60 border-r border-border bg-secondary flex flex-col sticky top-0 h-screen">
         <div className="h-14 flex items-center px-4 border-b border-border shrink-0">
           {logoUrl ? (
diff --git a/app/api/admin/auth/route.ts b/app/api/admin/auth/route.ts
index 21cf2a7a..509fa15d 100644
--- a/app/api/admin/auth/route.ts
+++ b/app/api/admin/auth/route.ts
@@ -7,24 +7,24 @@ import { logger } from '@/lib/logger';
 import { getStalwartCredentials } from '@/lib/stalwart/credentials';
 
 /**
- * Check if the current user is a Stalwart admin via principal roles.
+ * Check if the current user is a Stalwart admin by probing an admin-only endpoint.
  */
 async function checkStalwartAdmin(request: NextRequest): Promise<boolean> {
   try {
     const creds = await getStalwartCredentials(request);
     if (!creds) return false;
 
-    const response = await fetch(
-      `${creds.apiUrl}/api/principal/${encodeURIComponent(creds.username)}`,
-      { method: 'GET', headers: { 'Authorization': creds.authHeader } }
-    );
-    if (!response.ok) return false;
+    // Probe admin-only endpoint: listing principals requires admin privileges
+    const response = await fetch(`${creds.apiUrl}/api/principal?limit=1`, {
+      method: 'GET',
+      headers: { 'Authorization': creds.authHeader },
+    });
 
-    const data = await response.json();
-    const principal = data.data ?? data;
-    const roles: string[] = Array.isArray(principal?.roles) ? principal.roles : [];
-    return roles.includes('admin');
-  } catch {
+    const isAdmin = response.ok;
+    logger.info('Stalwart admin check (auth)', { username: creds.username, status: response.status, isAdmin });
+    return isAdmin;
+  } catch (error) {
+    logger.debug('Stalwart admin check error', { error: error instanceof Error ? error.message : 'Unknown' });
     return false;
   }
 }
diff --git a/app/api/admin/stalwart-check/route.ts b/app/api/admin/stalwart-check/route.ts
index 0f876534..fd067e26 100644
--- a/app/api/admin/stalwart-check/route.ts
+++ b/app/api/admin/stalwart-check/route.ts
@@ -4,8 +4,8 @@ import { getStalwartCredentials } from '@/lib/stalwart/credentials';
 
 /**
  * GET /api/admin/stalwart-check
- * Check if the currently logged-in user has the 'admin' role in Stalwart.
- * Uses the user's JMAP session credentials.
+ * Check if the currently logged-in user is a Stalwart admin.
+ * Probes the admin-only principal-list endpoint — if the user can access it, they're an admin.
  */
 export async function GET(request: NextRequest) {
   try {
@@ -16,24 +16,16 @@ export async function GET(request: NextRequest) {
       });
     }
 
-    const response = await fetch(
-      `${creds.apiUrl}/api/principal/${encodeURIComponent(creds.username)}`,
-      {
-        method: 'GET',
-        headers: { 'Authorization': creds.authHeader },
-      }
-    );
+    // Probe an admin-only endpoint: listing principals requires admin privileges.
+    // Use limit=1 to minimize payload.
+    const url = `${creds.apiUrl}/api/principal?limit=1`;
+    const response = await fetch(url, {
+      method: 'GET',
+      headers: { 'Authorization': creds.authHeader },
+    });
 
-    if (!response.ok) {
-      return NextResponse.json({ isStalwartAdmin: false }, {
-        headers: { 'Cache-Control': 'no-store' },
-      });
-    }
-
-    const data = await response.json();
-    const principal = data.data ?? data;
-    const roles: string[] = Array.isArray(principal?.roles) ? principal.roles : [];
-    const isStalwartAdmin = roles.includes('admin');
+    const isStalwartAdmin = response.ok;
+    logger.info('Stalwart admin check', { username: creds.username, status: response.status, isStalwartAdmin });
 
     return NextResponse.json({ isStalwartAdmin }, {
       headers: { 'Cache-Control': 'no-store' },
diff --git a/components/layout/navigation-rail.tsx b/components/layout/navigation-rail.tsx
index 3733ab56..c997a7d4 100644
--- a/components/layout/navigation-rail.tsx
+++ b/components/layout/navigation-rail.tsx
@@ -2,18 +2,20 @@
 
 import { useState, useRef, useEffect, useCallback } from "react";
 import { createPortal } from "react-dom";
-import { Mail, Calendar, BookUser, HardDrive, Settings, Keyboard, Plus } from "lucide-react";
+import { Mail, Calendar, BookUser, HardDrive, Settings, Keyboard, Plus, Shield } from "lucide-react";
 import { AccountSwitcher } from "./account-switcher";
 import { icons as lucideIcons, type LucideIcon } from "lucide-react";
 import { useConfig } from "@/hooks/use-config";
 import { useThemeStore } from "@/stores/theme-store";
 import { usePathname, Link } from "@/i18n/navigation";
+import NextLink from "next/link";
 import { useTranslations } from "next-intl";
 import { useCalendarStore } from "@/stores/calendar-store";
 import { useEmailStore } from "@/stores/email-store";
 import { useWebDAVStore } from "@/stores/webdav-store";
 import { useSettingsStore } from "@/stores/settings-store";
 import { usePolicyStore } from "@/stores/policy-store";
+import { useAuthStore } from "@/stores/auth-store";
 import { cn, formatFileSize } from "@/lib/utils";
 import { PluginSlot } from "@/components/plugins/plugin-slot";
 
@@ -165,6 +167,33 @@ export function NavigationRail({
   const sidebarAppsEnabled = usePolicyStore((s) => s.isFeatureEnabled('sidebarAppsEnabled'));
   const visibleSidebarApps = sidebarAppsEnabled ? sidebarApps : [];
   const inboxUnread = mailboxes.find(m => m.role === "inbox")?.unreadEmails || 0;
+  const [isStalwartAdmin, setIsStalwartAdmin] = useState(false);
+
+  useEffect(() => {
+    let cancelled = false;
+    const { client } = useAuthStore.getState();
+    if (!client) return;
+    const headers: Record<string, string> = {
+      'Authorization': client.getAuthHeader(),
+      'X-JMAP-Server-URL': client.getServerUrl(),
+      'X-JMAP-Username': client.getUsername(),
+    };
+    fetch('/api/admin/stalwart-check', { headers })
+      .then(res => res.json())
+      .then(data => {
+        if (!cancelled && data.isStalwartAdmin) {
+          setIsStalwartAdmin(true);
+          // Pre-create admin session so /admin works even after full page navigation
+          fetch('/api/admin/auth', {
+            method: 'POST',
+            headers: { 'Content-Type': 'application/json', ...headers },
+            body: JSON.stringify({ stalwartAuth: true }),
+          }).catch(() => {});
+        }
+      })
+      .catch(() => {});
+    return () => { cancelled = true; };
+  }, []);
 
   const navItems: NavItem[] = [
     { id: "mail", icon: Mail, labelKey: "mail", href: "/", badge: inboxUnread },
@@ -260,6 +289,21 @@ export function NavigationRail({
           );
         })}
 
+        {/* Admin (Stalwart admins) */}
+        {isStalwartAdmin && (
+          <NextLink
+            href="/admin"
+            className={cn(
+              "flex flex-col items-center justify-center gap-1 py-2 px-3 min-w-[64px] min-h-[44px] shrink-0",
+              "transition-colors duration-150",
+              "text-muted-foreground hover:text-foreground"
+            )}
+          >
+            <Shield className="w-5 h-5" />
+            <span className="text-[10px] font-medium leading-tight">{t("admin") || "Admin"}</span>
+          </NextLink>
+        )}
+
         {/* Settings */}
         <Link
           href="/settings"
@@ -420,8 +464,18 @@ export function NavigationRail({
 
       <PluginSlot name="navigation-rail-bottom" />
 
-      {/* Footer: Settings + Help + Storage Quota + Sign Out + Push Status */}
+      {/* Footer: Admin + Settings + Help + Storage Quota + Sign Out + Push Status */}
       <div className="mt-auto flex flex-col items-center gap-2 pb-3 px-1">
+        {isStalwartAdmin && (
+          <NextLink
+            href="/admin"
+            className="flex items-center justify-center w-10 h-10 rounded-md transition-colors text-muted-foreground hover:text-foreground hover:bg-muted"
+            title={t("admin") || "Admin"}
+          >
+            <Shield className="w-[18px] h-[18px]" />
+          </NextLink>
+        )}
+
         <Link
           href="/settings"
           onClick={activeAppId ? () => onCloseInlineApp?.() : undefined}
diff --git a/lib/stalwart/credentials.ts b/lib/stalwart/credentials.ts
index e17913f9..1580d44c 100644
--- a/lib/stalwart/credentials.ts
+++ b/lib/stalwart/credentials.ts
@@ -23,7 +23,8 @@ export interface StalwartCredentials {
  * (e.g. `https://admin.example.com`).
  */
 function getStalwartApiUrl(jmapServerUrl: string): string {
-  return process.env.STALWART_API_URL || jmapServerUrl;
+  const url = process.env.STALWART_API_URL || jmapServerUrl;
+  return url.replace(/\/+$/, '');
 }
 
 /**