diff --git a/backend/src/routes/mailboxes.ts b/backend/src/routes/mailboxes.ts
index 4025a88..612756a 100644
--- a/backend/src/routes/mailboxes.ts
+++ b/backend/src/routes/mailboxes.ts
@@ -135,8 +135,21 @@ mailboxesRouter.get('/:email/rules', async (req, res) => {
 mailboxesRouter.put('/:email/rules', async (req, res) => {
   const email = normalizeEmail(req.params.email);
   ensureDomain(req, domainFromEmail(email));
-  const body = z.object({ ooo_active: z.boolean().optional(), ooo_message: z.string().optional(), forwards: z.array(z.string().email()).optional() }).parse(req.body);
-  const saved = await dynamo.putRules({ email_address: email, ooo_active: body.ooo_active, ooo_message: body.ooo_message, forwards: body.forwards });
+  const body = z.object({
+    ooo_active: z.boolean().optional(),
+    ooo_message: z.string().optional(),
+    // 'text' or 'html'. Stored as-is in DynamoDB so the email worker can
+    // pick the correct Content-Type when sending the auto-reply.
+    ooo_content_type: z.enum(['text', 'html']).optional(),
+    forwards: z.array(z.string().email()).optional(),
+  }).parse(req.body);
+  const saved = await dynamo.putRules({
+    email_address: email,
+    ooo_active: body.ooo_active,
+    ooo_message: body.ooo_message,
+    ooo_content_type: body.ooo_content_type,
+    forwards: body.forwards,
+  });
   await audit(req.user!.email, 'mailbox.rules_update', 'mailbox', email, saved, req.ip);
   res.json(saved);
 });
diff --git a/backend/src/services/dynamodb.ts b/backend/src/services/dynamodb.ts
index 69ec7f2..ef47609 100644
--- a/backend/src/services/dynamodb.ts
+++ b/backend/src/services/dynamodb.ts
@@ -7,7 +7,9 @@ export interface EmailRule {
   email_address: string;
   ooo_active?: boolean;
   ooo_message?: string;
-  ooo_content_type?: string;
+  // 'text' or 'html' — kept consistent with the config-email app that
+  // shares the same DynamoDB table so both apps interpret it the same way.
+  ooo_content_type?: 'text' | 'html';
   forwards?: string[];
 }
 
@@ -16,6 +18,13 @@ export interface BlockList {
   blocked_patterns: string[];
 }
 
+// Tolerate legacy values that may already exist in DynamoDB.
+function normalizeContentType(v: unknown): 'text' | 'html' {
+  const s = String(v ?? '').toLowerCase();
+  if (s === 'html' || s === 'text/html') return 'html';
+  return 'text';
+}
+
 export class DynamoRulesService {
   private doc = DynamoDBDocumentClient.from(new DynamoDBClient({ region: config.awsRegion }), {
     marshallOptions: { removeUndefinedValues: true },
@@ -24,7 +33,14 @@ export class DynamoRulesService {
   async getRules(email: string): Promise<EmailRule> {
     const email_address = normalizeEmail(email);
     const resp = await this.doc.send(new GetCommand({ TableName: config.rulesTable, Key: { email_address } }));
-    return (resp.Item as EmailRule) ?? { email_address, ooo_active: false, ooo_message: '', ooo_content_type: 'text/plain', forwards: [] };
+    const item = resp.Item as EmailRule | undefined;
+    if (!item) {
+      return { email_address, ooo_active: false, ooo_message: '', ooo_content_type: 'text', forwards: [] };
+    }
+    return {
+      ...item,
+      ooo_content_type: normalizeContentType(item.ooo_content_type),
+    };
   }
 
   async putRules(rule: EmailRule): Promise<EmailRule> {
@@ -32,7 +48,7 @@ export class DynamoRulesService {
       email_address: normalizeEmail(rule.email_address),
       ooo_active: !!rule.ooo_active,
       ooo_message: rule.ooo_message ?? '',
-      ooo_content_type: rule.ooo_content_type ?? 'text/plain',
+      ooo_content_type: normalizeContentType(rule.ooo_content_type),
       forwards: (rule.forwards ?? []).map(normalizeEmail).filter(Boolean),
     };
     await this.doc.send(new PutCommand({ TableName: config.rulesTable, Item: item }));
@@ -57,4 +73,4 @@ export class DynamoRulesService {
     await this.doc.send(new PutCommand({ TableName: config.blockedTable, Item: item }));
     return item;
   }
-}
+}
\ No newline at end of file
diff --git a/frontend/src/components/MailboxSettingsModal.jsx b/frontend/src/components/MailboxSettingsModal.jsx
index 24cf3b9..c93f9d2 100644
--- a/frontend/src/components/MailboxSettingsModal.jsx
+++ b/frontend/src/components/MailboxSettingsModal.jsx
@@ -13,6 +13,14 @@ const TABS = [
   { id: 'block', label: 'Blocklist', icon: FiSlash },
 ];
 
+const emptyRule = (email) => ({
+  email_address: email,
+  ooo_active: false,
+  ooo_message: '',
+  ooo_content_type: 'text',
+  forwards: [],
+});
+
 const MailboxSettingsModal = ({ open, email, initialTab = 'fwd', onClose, onToast }) => {
   const [activeTab, setActiveTab] = useState(initialTab);
   const [rule, setRule] = useState(null);
@@ -29,15 +37,13 @@ const MailboxSettingsModal = ({ open, email, initialTab = 'fwd', onClose, onToas
       setLoading(true);
       try {
         const [r, b] = await Promise.all([
-          mailboxesAPI.getRules(email).catch(() => ({
-            email_address: email, ooo_active: false, ooo_message: '', forwards: [],
-          })),
+          mailboxesAPI.getRules(email).catch(() => emptyRule(email)),
           mailboxesAPI.getBlocklist(email).catch(() => ({
             email_address: email, blocked_patterns: [],
           })),
         ]);
         if (cancelled) return;
-        setRule(r || { email_address: email, ooo_active: false, ooo_message: '', forwards: [] });
+        setRule(r ? { ...emptyRule(email), ...r } : emptyRule(email));
         setBlocklist(b || { email_address: email, blocked_patterns: [] });
       } catch (err) {
         if (!cancelled) onToast?.(`Failed to load settings: ${err.message}`, 'error');
@@ -50,10 +56,12 @@ const MailboxSettingsModal = ({ open, email, initialTab = 'fwd', onClose, onToas
 
   // Merge updates with existing rule and persist.
   const saveRule = async (updates) => {
+    const base = rule || emptyRule(email);
     const merged = {
-      ooo_active: rule?.ooo_active ?? false,
-      ooo_message: rule?.ooo_message ?? '',
-      forwards: rule?.forwards ?? [],
+      ooo_active: base.ooo_active ?? false,
+      ooo_message: base.ooo_message ?? '',
+      ooo_content_type: base.ooo_content_type ?? 'text',
+      forwards: base.forwards ?? [],
       ...updates,
     };
     try {
@@ -127,4 +135,4 @@ const MailboxSettingsModal = ({ open, email, initialTab = 'fwd', onClose, onToas
   );
 };
 
-export default MailboxSettingsModal;
+export default MailboxSettingsModal;
\ No newline at end of file
diff --git a/frontend/src/components/OutOfOffice.jsx b/frontend/src/components/OutOfOffice.jsx
index 4e3ac58..781de6f 100644
--- a/frontend/src/components/OutOfOffice.jsx
+++ b/frontend/src/components/OutOfOffice.jsx
@@ -1,15 +1,22 @@
 import React, { useState } from 'react';
-import { FiCalendar } from 'react-icons/fi';
+import { FiCalendar, FiFileText } from 'react-icons/fi';
 
 const OutOfOffice = ({ rule, onSave }) => {
   const [isActive, setIsActive] = useState(rule?.ooo_active || false);
   const [message, setMessage] = useState(rule?.ooo_message || '');
+  const [contentType, setContentType] = useState(
+    rule?.ooo_content_type === 'html' ? 'html' : 'text'
+  );
   const [isSaving, setIsSaving] = useState(false);
 
   const handleSave = async () => {
     setIsSaving(true);
     try {
-      await onSave({ ooo_active: isActive, ooo_message: message });
+      await onSave({
+        ooo_active: isActive,
+        ooo_message: message,
+        ooo_content_type: contentType,
+      });
     } finally {
       setIsSaving(false);
     }
@@ -17,6 +24,7 @@ const OutOfOffice = ({ rule, onSave }) => {
 
   return (
     <div className="space-y-6">
+      {/* Toggle Active/Inactive */}
       <div className="flex items-center justify-between p-4 bg-gray-50 rounded-lg border border-gray-200">
         <div className="flex items-center gap-3">
           <FiCalendar className="w-5 h-5 text-gray-600" />
@@ -43,6 +51,40 @@ const OutOfOffice = ({ rule, onSave }) => {
         </button>
       </div>
 
+      {/* Content Type Selector */}
+      <div>
+        <label className="block text-sm font-semibold text-gray-700 mb-2">
+          Message Format
+        </label>
+        <div className="flex gap-2">
+          <button
+            type="button"
+            onClick={() => setContentType('text')}
+            className={`flex-1 px-4 py-2 rounded-lg border-2 transition-all ${
+              contentType === 'text'
+                ? 'border-primary-600 bg-primary-50 text-primary-700 font-semibold'
+                : 'border-gray-300 bg-white text-gray-700 hover:border-gray-400'
+            }`}
+          >
+            <FiFileText className="inline w-4 h-4 mr-2" />
+            Plain Text
+          </button>
+          <button
+            type="button"
+            onClick={() => setContentType('html')}
+            className={`flex-1 px-4 py-2 rounded-lg border-2 transition-all ${
+              contentType === 'html'
+                ? 'border-primary-600 bg-primary-50 text-primary-700 font-semibold'
+                : 'border-gray-300 bg-white text-gray-700 hover:border-gray-400'
+            }`}
+          >
+            <span className="font-mono text-sm mr-2">&lt;/&gt;</span>
+            HTML
+          </button>
+        </div>
+      </div>
+
+      {/* Message Editor */}
       <div>
         <label htmlFor="ooo-message" className="block text-sm font-semibold text-gray-700 mb-2">
           Auto-Reply Message
@@ -52,22 +94,36 @@ const OutOfOffice = ({ rule, onSave }) => {
           value={message}
           onChange={(e) => setMessage(e.target.value)}
           rows={8}
-          placeholder="I am currently out of office until [date].&#10;&#10;Best regards,&#10;Your Name"
+          placeholder={
+            contentType === 'html'
+              ? '<p>I am currently out of office until [date].</p>\n<p>Best regards,<br>Your Name</p>'
+              : 'I am currently out of office until [date].\n\nBest regards,\nYour Name'
+          }
           className="input-field font-mono text-sm resize-none"
           disabled={!isActive}
         />
         <p className="mt-2 text-xs text-gray-500">
-          Plain text message that gets returned automatically to senders.
+          {contentType === 'html'
+            ? 'You can use HTML tags for formatting. The reply will be sent as text/html.'
+            : 'Plain text message that gets returned automatically to senders.'}
         </p>
       </div>
 
+      {/* Message Preview */}
       {isActive && message && (
         <div>
           <label className="block text-sm font-semibold text-gray-700 mb-2">
             Message Preview
           </label>
           <div className="p-4 bg-gray-50 border border-gray-200 rounded-lg">
-            <pre className="text-sm text-gray-800 whitespace-pre-wrap font-sans">{message}</pre>
+            {contentType === 'html' ? (
+              <div
+                className="prose prose-sm max-w-none text-sm text-gray-800"
+                dangerouslySetInnerHTML={{ __html: message }}
+              />
+            ) : (
+              <pre className="text-sm text-gray-800 whitespace-pre-wrap font-sans">{message}</pre>
+            )}
           </div>
         </div>
       )}
@@ -85,4 +141,4 @@ const OutOfOffice = ({ rule, onSave }) => {
   );
 };
 
-export default OutOfOffice;
+export default OutOfOffice;
\ No newline at end of file