diff --git a/app/(main)/[locale]/login/page.tsx b/app/(main)/[locale]/login/page.tsx
index 0ef6ccd7..953195f4 100644
--- a/app/(main)/[locale]/login/page.tsx
+++ b/app/(main)/[locale]/login/page.tsx
@@ -11,7 +11,7 @@ import { useAccountStore } from "@/stores/account-store";
 import { useThemeStore } from "@/stores/theme-store";
 import { useShallow } from "zustand/react/shallow";
 import { useConfig } from "@/hooks/use-config";
-import { apiFetch, getPathPrefix } from "@/lib/browser-navigation";
+import { apiFetch, getPathPrefix, withBasePath } from "@/lib/browser-navigation";
 import { cn } from "@/lib/utils";
 import { AlertCircle, Loader2, X, Info, Eye, EyeOff, LogIn, Sun, Moon, Monitor, Check, Shield, Play, Copy } from "lucide-react";
 import { discoverOAuth, type OAuthMetadata } from "@/lib/oauth/discovery";
@@ -722,7 +722,7 @@ export default function LoginPage() {
             <div className="px-8 pt-12 pb-4 text-center">
               <div className="inline-flex items-center justify-center w-20 h-20 mb-6">
                 <img
-                  src={resolvedTheme === 'dark' ? loginLogoDarkUrl : loginLogoLightUrl}
+                  src={withBasePath(resolvedTheme === 'dark' ? loginLogoDarkUrl : loginLogoLightUrl)}
                   alt={appName}
                   className="max-w-20 max-h-20 object-contain"
                 />
@@ -872,7 +872,7 @@ export default function LoginPage() {
           <div className="px-8 pt-10 pb-6 text-center">
             <div className="inline-flex items-center justify-center w-16 h-16 mb-5">
               <img
-                src={resolvedTheme === 'dark' ? loginLogoDarkUrl : loginLogoLightUrl}
+                src={withBasePath(resolvedTheme === 'dark' ? loginLogoDarkUrl : loginLogoLightUrl)}
                 alt={appName}
                 className="max-w-16 max-h-16 object-contain"
               />
diff --git a/app/(main)/admin/layout.tsx b/app/(main)/admin/layout.tsx
index a792703a..19fd9020 100644
--- a/app/(main)/admin/layout.tsx
+++ b/app/(main)/admin/layout.tsx
@@ -32,7 +32,7 @@ import { useThemeStore } from '@/stores/theme-store';
 import { getActiveAccountSlotHeaders } from '@/lib/auth/active-account-slot';
 
 import { useUpdateStore, selectHasUpdate } from '@/stores/update-store';
-import { apiFetch, getPathPrefix } from '@/lib/browser-navigation';
+import { apiFetch, getPathPrefix, withBasePath } from '@/lib/browser-navigation';
 
 // Single-page tab navigation: clicks update a Zustand store. The URL stays
 // at /admin so React doesn't fire a route transition on every tab switch -
@@ -90,9 +90,9 @@ export default function AdminLayout({ children }: { children: React.ReactNode })
   const { appLogoLightUrl, appLogoDarkUrl, loginLogoLightUrl, loginLogoDarkUrl } = useConfig();
   const filesEnabled = usePolicyStore((s) => s.isFeatureEnabled('filesEnabled'));
   const resolvedTheme = useThemeStore((s) => s.resolvedTheme);
-  const logoUrl = resolvedTheme === 'dark'
+  const logoUrl = withBasePath(resolvedTheme === 'dark'
     ? (appLogoDarkUrl || appLogoLightUrl || loginLogoDarkUrl)
-    : (appLogoLightUrl || appLogoDarkUrl || loginLogoLightUrl);
+    : (appLogoLightUrl || appLogoDarkUrl || loginLogoLightUrl));
 
   // Match the navigation rail: red for security/deprecated, amber for normal.
   const hasUpdate = useUpdateStore(selectHasUpdate);
diff --git a/app/(main)/admin/login/page.tsx b/app/(main)/admin/login/page.tsx
index 9f57f3b3..018777d4 100644
--- a/app/(main)/admin/login/page.tsx
+++ b/app/(main)/admin/login/page.tsx
@@ -5,7 +5,7 @@ import { useRouter } from 'next/navigation';
 import { Shield } from 'lucide-react';
 import { useConfig } from '@/hooks/use-config';
 import { useThemeStore } from '@/stores/theme-store';
-import { apiFetch } from '@/lib/browser-navigation';
+import { apiFetch, withBasePath } from '@/lib/browser-navigation';
 
 export default function AdminLoginPage() {
   const router = useRouter();
@@ -14,7 +14,7 @@ export default function AdminLoginPage() {
   const [loading, setLoading] = useState(false);
   const { loginLogoLightUrl, loginLogoDarkUrl } = useConfig();
   const resolvedTheme = useThemeStore((s) => s.resolvedTheme);
-  const logoUrl = resolvedTheme === 'dark' ? loginLogoDarkUrl : loginLogoLightUrl;
+  const logoUrl = withBasePath(resolvedTheme === 'dark' ? loginLogoDarkUrl : loginLogoLightUrl);
 
   async function handleSubmit(e: FormEvent) {
     e.preventDefault();
diff --git a/app/(main)/layout.tsx b/app/(main)/layout.tsx
index b98b064c..ac5c3b42 100644
--- a/app/(main)/layout.tsx
+++ b/app/(main)/layout.tsx
@@ -5,6 +5,7 @@ import { getLocale } from "next-intl/server";
 import { PWAInstallPrompt } from "@/components/pwa-install-prompt";
 import { ServiceWorkerRegistration } from "@/components/service-worker-registration";
 import { configManager } from "@/lib/admin/config-manager";
+import { withBasePath } from "@/lib/browser-navigation";
 import "../globals.css";
 
 const geistSans = Geist({
@@ -38,7 +39,7 @@ export async function generateMetadata(): Promise<Metadata> {
     formatDetection: {
       telephone: false,
     },
-    icons: { icon: faviconUrl },
+    icons: { icon: withBasePath(faviconUrl) },
   };
 }
 
diff --git a/app/(main)/setup/page.tsx b/app/(main)/setup/page.tsx
index 686bb202..c40664f5 100644
--- a/app/(main)/setup/page.tsx
+++ b/app/(main)/setup/page.tsx
@@ -3,7 +3,7 @@
 import { useEffect, useState, type FormEvent, type ReactNode } from 'react';
 import { useRouter, useSearchParams } from 'next/navigation';
 import { CheckCircle2, AlertTriangle, AlertCircle, Server, ShieldCheck, KeyRound, FileText, Palette, Lock, ShieldAlert } from 'lucide-react';
-import { apiFetch, getPathPrefix } from '@/lib/browser-navigation';
+import { apiFetch, getPathPrefix, withBasePath } from '@/lib/browser-navigation';
 
 type State = 'bootstrap' | 'configured' | 'env-managed';
 
@@ -1329,7 +1329,7 @@ function BrandingAsset({
             }}
           />
           {value ? (
-            <img src={value} alt="" className="max-w-full max-h-full object-contain" />
+            <img src={withBasePath(value)} alt="" className="max-w-full max-h-full object-contain" />
           ) : (
             <span className="text-[10px] text-muted-foreground text-center px-1">click or drop</span>
           )}
diff --git a/components/email/email-viewer.tsx b/components/email/email-viewer.tsx
index 364e3b30..1be0569b 100644
--- a/components/email/email-viewer.tsx
+++ b/components/email/email-viewer.tsx
@@ -7,6 +7,7 @@ import { emailExportFilename, attachmentDownloadFilename, DEFAULT_EMAIL_TEMPLATE
 import { EML_IMPORT_ACCEPT, expandImportableEmails } from "@/lib/eml-import";
 import { EMAIL_IFRAME_SANITIZE_CONFIG, collapseBlockedImageContainers, escapeHtml, plainTextToSafeHtml, sanitizeEmailHtml, sanitizePlainTextRenderedHtml } from "@/lib/email-sanitization";
 import { hasMeaningfulHtmlBody } from "@/lib/signature-utils";
+import { withBasePath } from "@/lib/browser-navigation";
 import { Button } from "@/components/ui/button";
 import { Avatar } from "@/components/ui/avatar";
 import { formatFileSize, cn, buildMailboxTree, MailboxNode, formatDateTime, generateUUID } from "@/lib/utils";
@@ -3270,9 +3271,9 @@ export function EmailViewer({
 
   if (!email) {
     if (isDemoMode) {
-      const logoSrc = resolvedTheme === 'dark'
+      const logoSrc = withBasePath(resolvedTheme === 'dark'
         ? '/branding/Bulwark_Logo_with_Lettering_White_and_Color.svg'
-        : '/branding/Bulwark_Logo_with_Lettering_Dark_Color.svg';
+        : '/branding/Bulwark_Logo_with_Lettering_Dark_Color.svg');
       return (
         <div className={cn("flex-1 flex flex-col items-center justify-center bg-gradient-to-br from-muted/30 to-muted/50", className)}>
           <div className="text-center p-8 max-w-md">
diff --git a/components/layout/navigation-rail.tsx b/components/layout/navigation-rail.tsx
index 56a721d9..fc6649ff 100644
--- a/components/layout/navigation-rail.tsx
+++ b/components/layout/navigation-rail.tsx
@@ -21,7 +21,7 @@ import { getMaxAccounts } from "@/lib/account-utils";
 import { cn, formatFileSize } from "@/lib/utils";
 import { PluginSlot } from "@/components/plugins/plugin-slot";
 import { KeyboardShortcutsModal } from "@/components/keyboard-shortcuts-modal";
-import { apiFetch, getPathPrefix } from "@/lib/browser-navigation";
+import { apiFetch, getPathPrefix, withBasePath } from "@/lib/browser-navigation";
 import { Avatar } from "@/components/ui/avatar";
 
 interface NavItem {
@@ -444,7 +444,7 @@ export function NavigationRail({
       )}
     >
       {(() => {
-        const logoUrl = resolvedTheme === 'dark' ? (appLogoDarkUrl || appLogoLightUrl) : (appLogoLightUrl || appLogoDarkUrl);
+        const logoUrl = withBasePath(resolvedTheme === 'dark' ? (appLogoDarkUrl || appLogoLightUrl) : (appLogoLightUrl || appLogoDarkUrl));
         return logoUrl ? (
           <div className="flex items-center justify-center py-3 px-1">
             <img
diff --git a/components/pwa-install-prompt.tsx b/components/pwa-install-prompt.tsx
index cb21f7e1..00c8bfb3 100644
--- a/components/pwa-install-prompt.tsx
+++ b/components/pwa-install-prompt.tsx
@@ -3,6 +3,7 @@
 import { useEffect, useState } from "react";
 import { X, Download } from "lucide-react";
 import { useConfig } from "@/hooks/use-config";
+import { withBasePath } from "@/lib/browser-navigation";
 
 interface BeforeInstallPromptEvent extends Event {
   prompt: () => Promise<void>;
@@ -58,7 +59,8 @@ export function PWAInstallPrompt() {
     return null;
   }
 
-  const logoSrc = appLogoLightUrl || faviconUrl;
+  const logoSrc = withBasePath(appLogoLightUrl || faviconUrl);
+  const darkLogoSrc = withBasePath(appLogoDarkUrl || faviconUrl);
 
   return (
     <div className="fixed bottom-4 right-4 z-50 bg-white dark:bg-neutral-900 rounded-lg shadow-lg border border-neutral-200 dark:border-neutral-800 p-4 max-w-sm animate-in slide-in-from-bottom-4">
@@ -75,7 +77,7 @@ export function PWAInstallPrompt() {
           )}
           {logoSrc && (
             <img
-              src={appLogoDarkUrl || faviconUrl}
+              src={darkLogoSrc}
               alt={appName}
               className="w-8 h-8 shrink-0 object-contain hidden dark:block"
             />
diff --git a/components/settings/files-settings.tsx b/components/settings/files-settings.tsx
index 1bec3ddd..c686684a 100644
--- a/components/settings/files-settings.tsx
+++ b/components/settings/files-settings.tsx
@@ -6,6 +6,7 @@ import { Folder, FolderOpen, FileText, FileCode, ImageIcon, FileAudio, File, Hom
 import { SettingsSection, SettingItem, ToggleSwitch, RadioGroup } from "./settings-section";
 import { loadFilesSettings, saveFilesSettings, type FilesSettings, type FolderLayout } from "@/components/files/files-settings-dialog";
 import { cn } from "@/lib/utils";
+import { withBasePath } from "@/lib/browser-navigation";
 
 interface SampleFile {
   name: string;
@@ -95,7 +96,7 @@ function FilesSettingsPreview({ settings }: { settings: FilesSettings }) {
           )}
         >
           {settings.showThumbnails && file.thumbnailUrl ? (
-            <img src={file.thumbnailUrl} alt="" className="w-4 h-4 rounded object-cover flex-shrink-0" />
+            <img src={withBasePath(file.thumbnailUrl)} alt="" className="w-4 h-4 rounded object-cover flex-shrink-0" />
           ) : settings.showIcons ? (
             getPreviewIcon(file, settings.coloredIcons, "sm")
           ) : null}
@@ -125,7 +126,7 @@ function FilesSettingsPreview({ settings }: { settings: FilesSettings }) {
             )}
           >
             {settings.showThumbnails && file.thumbnailUrl ? (
-              <img src={file.thumbnailUrl} alt="" className="w-8 h-8 rounded object-cover flex-shrink-0" />
+              <img src={withBasePath(file.thumbnailUrl)} alt="" className="w-8 h-8 rounded object-cover flex-shrink-0" />
             ) : settings.showIcons ? (
               getPreviewIcon(file, settings.coloredIcons, "lg")
             ) : (
diff --git a/components/ui/avatar.tsx b/components/ui/avatar.tsx
index 13ac7c20..315aa53e 100644
--- a/components/ui/avatar.tsx
+++ b/components/ui/avatar.tsx
@@ -6,6 +6,7 @@ import { useSettingsStore } from "@/stores/settings-store";
 import { useContactStore, getContactPhotoUri } from "@/stores/contact-store";
 import { useConfig } from "@/hooks/use-config";
 import { avatarHooks } from "@/lib/plugin-hooks";
+import { withBasePath } from "@/lib/browser-navigation";
 
 const IS_DEV = process.env.NODE_ENV !== "production";
 
@@ -236,7 +237,7 @@ export function Avatar({ name, email, contactPhotoUri, size = "md", className, d
   const customAvatar = devMode && email ? CUSTOM_AVATARS[email.toLowerCase()] : null;
   const pluginAvatar = pluginAvatarFailed ? null : pluginAvatarUrl;
   const photoSrc = resolvedContactPhoto || pluginAvatar || customAvatar || profilePic || null;
-  const faviconSrc = !imgError && !domainFailed && showFavicon ? `/api/favicon?domain=${encodeURIComponent(faviconDomain!)}` : null;
+  const faviconSrc = !imgError && !domainFailed && showFavicon ? withBasePath(`/api/favicon?domain=${encodeURIComponent(faviconDomain!)}`) : null;
   const imgSrc = disableImages ? null : (photoSrc || faviconSrc);
   const isFavicon = imgSrc !== null && imgSrc === faviconSrc;
 
diff --git a/lib/browser-navigation.ts b/lib/browser-navigation.ts
index 5df6ff91..15369273 100644
--- a/lib/browser-navigation.ts
+++ b/lib/browser-navigation.ts
@@ -75,6 +75,26 @@ export function apiFetch(input: string, init?: RequestInit): Promise<Response> {
   return fetch(input, init);
 }
 
+/**
+ * Mount-prefix-aware wrapper for URL strings used in `<img src>`, `<link href>`,
+ * `window.location.*`, etc. — anything the browser resolves itself, where
+ * `apiFetch` can't help.
+ *
+ * Idempotent: passing an already-prefixed value, an external URL, a
+ * protocol-relative URL, or an empty/falsy value returns it unchanged. So it's
+ * safe to wrap admin-configurable values that might be either a local path
+ * (`/branding/foo.svg`, `/api/admin/branding/...`) or a full URL.
+ */
+export function withBasePath(url: string | null | undefined): string {
+  if (!url) return url ?? '';
+  if (url.charCodeAt(0) !== 47) return url;        // not absolute (e.g. https://, data:, blob:)
+  if (url.charCodeAt(1) === 47) return url;        // protocol-relative //cdn...
+  const prefix = getPathPrefix();
+  if (!prefix) return url;
+  if (url === prefix || url.startsWith(prefix + '/')) return url;
+  return prefix + url;
+}
+
 
 /**
  * Extracts the locale from the current URL, skipping any mount prefix.
diff --git a/lib/webdav/client.ts b/lib/webdav/client.ts
index 2772d37d..05486798 100644
--- a/lib/webdav/client.ts
+++ b/lib/webdav/client.ts
@@ -4,6 +4,7 @@
  */
 
 import { getActiveAccountSlotHeaders } from '@/lib/auth/active-account-slot';
+import { apiFetch, withBasePath } from '@/lib/browser-navigation';
 
 export interface WebDAVResource {
   href: string;
@@ -32,7 +33,7 @@ export class WebDAVClient {
       ...options?.headers,
     };
 
-    return fetch(this.proxyUrl, {
+    return apiFetch(this.proxyUrl, {
       method: 'POST',
       headers,
       body: options?.body,
@@ -118,7 +119,7 @@ export class WebDAVClient {
       // Use XMLHttpRequest for progress tracking
       return new Promise((resolve, reject) => {
         const xhr = new XMLHttpRequest();
-        xhr.open('POST', this.proxyUrl);
+        xhr.open('POST', withBasePath(this.proxyUrl));
         xhr.setRequestHeader('X-WebDAV-Method', 'PUT');
         xhr.setRequestHeader('X-WebDAV-Path', path);
         const slotHeaders = getActiveAccountSlotHeaders();