diff --git a/stores/__tests__/contact-store.test.ts b/stores/__tests__/contact-store.test.ts
index dd9dbec7..cd469e06 100644
--- a/stores/__tests__/contact-store.test.ts
+++ b/stores/__tests__/contact-store.test.ts
@@ -31,6 +31,8 @@ const defaultState = {
   supportsSync: false,
   selectedContactIds: new Set<string>(),
   activeTab: 'all' as const,
+  directoryPrincipals: [],
+  directoryLoaded: false,
 };
 
 describe('contact-store', () => {
@@ -273,6 +275,28 @@ describe('contact-store', () => {
       const results = useContactStore.getState().getAutocomplete('Multi');
       expect(results).toHaveLength(2);
     });
+
+    it('should augment results with directory principals', () => {
+      useContactStore.setState({
+        contacts: [],
+        directoryPrincipals: [{ name: 'Dana Director', email: 'dana@example.com' }],
+      });
+      const results = useContactStore.getState().getAutocomplete('dana');
+      expect(results).toHaveLength(1);
+      expect(results[0]).toEqual({ name: 'Dana Director', email: 'dana@example.com' });
+    });
+
+    it('should not duplicate a directory principal already matched as a contact', () => {
+      useContactStore.setState({
+        contacts: [
+          makeContact({ id: 'c1', name: { components: [{ kind: 'given', value: 'Jane' }], isOrdered: true }, emails: { e0: { address: 'jane@example.com' } } }),
+        ],
+        directoryPrincipals: [{ name: 'Jane From Directory', email: 'JANE@example.com' }],
+      });
+      const results = useContactStore.getState().getAutocomplete('jane');
+      expect(results).toHaveLength(1);
+      expect(results[0].name).toBe('Jane');
+    });
   });
 
   describe('getGroups', () => {
diff --git a/stores/auth-store.ts b/stores/auth-store.ts
index 5b7fcd9c..4aa67f60 100644
--- a/stores/auth-store.ts
+++ b/stores/auth-store.ts
@@ -239,6 +239,13 @@ function initializeFeatureStores(client: IJMAPClient): void {
     useContactStore.getState().setSupportsSync(false);
   }
 
+  // Directory (RFC 9670 principals) is independent of contacts support and only
+  // works when the server allows directory queries; populates recipient
+  // autocomplete with other users on the server.
+  if (client.supportsPrincipals()) {
+    useContactStore.getState().fetchDirectory(client).catch((err) => debug.error('Failed to fetch directory:', err));
+  }
+
   const vacationStore = useVacationStore.getState();
   if (client.supportsVacationResponse()) {
     vacationStore.setSupported(true);
diff --git a/stores/contact-store.ts b/stores/contact-store.ts
index a6159235..27ee111a 100644
--- a/stores/contact-store.ts
+++ b/stores/contact-store.ts
@@ -159,7 +159,13 @@ interface ContactStore {
   lastSelectedContactId: string | null;
   activeTab: 'all' | 'groups';
 
+  // Directory (RFC 9670 principals) — other users/groups on the server, used to
+  // augment recipient autocomplete. Runtime only, not persisted.
+  directoryPrincipals: Array<{ name: string; email: string; description?: string }>;
+  directoryLoaded: boolean;
+
   fetchContacts: (client: IJMAPClient) => Promise<void>;
+  fetchDirectory: (client: IJMAPClient) => Promise<void>;
   fetchAddressBooks: (client: IJMAPClient) => Promise<void>;
   fetchAllAccountsContacts: (accounts: ContactAccountClient[], activeLocalAccountId: string) => Promise<void>;
   fetchAllAccountsAddressBooks: (accounts: ContactAccountClient[], activeLocalAccountId: string) => Promise<void>;
@@ -258,6 +264,8 @@ export const useContactStore = create<ContactStore>()(
       selectedContactIds: new Set<string>(),
       lastSelectedContactId: null,
       activeTab: 'all' as const,
+      directoryPrincipals: [],
+      directoryLoaded: false,
 
       fetchContacts: async (client) => {
         set({ isLoading: true, error: null });
@@ -270,6 +278,28 @@ export const useContactStore = create<ContactStore>()(
         }
       },
 
+      fetchDirectory: async (client) => {
+        if (!client.supportsPrincipals()) return;
+        try {
+          const principals = await client.getPrincipals();
+          const entries: Array<{ name: string; email: string; description?: string }> = [];
+          for (const p of principals) {
+            // Stalwart reports a principal's account name in `email`; only those
+            // with an address are usable as recipients.
+            const email = p.email?.trim();
+            if (!email) continue;
+            entries.push({
+              name: p.name || email,
+              email,
+              description: p.description ?? undefined,
+            });
+          }
+          set({ directoryPrincipals: entries, directoryLoaded: true });
+        } catch (error) {
+          debug.error('Failed to fetch directory principals:', error);
+        }
+      },
+
       fetchAddressBooks: async (client) => {
         try {
           const addressBooks = await client.getAllAddressBooks();
@@ -474,6 +504,8 @@ export const useContactStore = create<ContactStore>()(
         error: null,
         selectedContactIds: new Set<string>(),
         activeTab: 'all',
+        directoryPrincipals: [],
+        directoryLoaded: false,
       }),
 
       getAutocomplete: (query) => {
@@ -516,6 +548,22 @@ export const useContactStore = create<ContactStore>()(
           if (results.length >= 10) break;
         }
 
+        // Augment with directory principals (other users on the server, RFC 9670).
+        // Contacts take precedence, so skip any address already suggested.
+        const { directoryPrincipals } = get();
+        if (directoryPrincipals.length > 0) {
+          const seen = new Set(results.map(r => r.email.toLowerCase()));
+          for (const p of directoryPrincipals) {
+            if (results.length >= 10) break;
+            const addr = p.email.toLowerCase();
+            if (seen.has(addr)) continue;
+            if (p.name.toLowerCase().includes(lower) || addr.includes(lower)) {
+              results.push({ name: p.name, email: p.email });
+              seen.add(addr);
+            }
+          }
+        }
+
         return results;
       },