diff --git a/apps/x/apps/main/src/ipc.ts b/apps/x/apps/main/src/ipc.ts
index 78f8b55e..f4f4fa66 100644
--- a/apps/x/apps/main/src/ipc.ts
+++ b/apps/x/apps/main/src/ipc.ts
@@ -47,7 +47,7 @@ import { summarizeMeeting } from '@x/core/dist/knowledge/summarize_meeting.js';
 import { getAccessToken } from '@x/core/dist/auth/tokens.js';
 import { getRowboatConfig } from '@x/core/dist/config/rowboat.js';
 import { runLiveNoteAgent } from '@x/core/dist/knowledge/live-note/runner.js';
-import { listImportantThreads, listEverythingElseThreads, saveMessageBodyHeight, triggerSync as triggerGmailSync } from '@x/core/dist/knowledge/sync_gmail.js';
+import { listImportantThreads, listEverythingElseThreads, saveMessageBodyHeight, triggerSync as triggerGmailSync, sendThreadReply } from '@x/core/dist/knowledge/sync_gmail.js';
 import { liveNoteBus } from '@x/core/dist/knowledge/live-note/bus.js';
 import { getInstallationId } from '@x/core/dist/analytics/installation.js';
 import { API_URL } from '@x/core/dist/config/env.js';
@@ -493,6 +493,9 @@ export function setupIpcHandlers() {
       triggerGmailSync();
       return {};
     },
+    'gmail:sendReply': async (_event, args) => {
+      return sendThreadReply(args);
+    },
     'gmail:saveMessageHeight': async (_event, args) => {
       saveMessageBodyHeight(args.threadId, args.messageId, args.height);
       return {};
diff --git a/apps/x/apps/renderer/src/components/email-view.tsx b/apps/x/apps/renderer/src/components/email-view.tsx
index 69f9b91e..1f555901 100644
--- a/apps/x/apps/renderer/src/components/email-view.tsx
+++ b/apps/x/apps/renderer/src/components/email-view.tsx
@@ -555,39 +555,55 @@ function ComposeBox({
     if (editor && sel) editor.chain().focus().setTextSelection(sel).run()
   }
 
+  const [sending, setSending] = useState(false)
   const sendInGmail = async () => {
-    if (!editor) {
-      window.open(thread.threadUrl, '_blank')
-      return
-    }
+    if (!editor || sending) return
     const html = editor.getHTML()
     const text = editor.getText().trim()
-
-    let copied = false
-    if (text) {
-      try {
-        if (typeof ClipboardItem !== 'undefined' && navigator.clipboard?.write) {
-          await navigator.clipboard.write([
-            new ClipboardItem({
-              'text/html': new Blob([html], { type: 'text/html' }),
-              'text/plain': new Blob([text], { type: 'text/plain' }),
-            }),
-          ])
-          copied = true
-        } else if (navigator.clipboard?.writeText) {
-          await navigator.clipboard.writeText(text)
-          copied = true
-        }
-      } catch (err) {
-        console.warn('[Gmail] clipboard write failed:', err)
-      }
+    if (!text) {
+      toast('Draft is empty.', 'error')
+      return
     }
 
-    window.open(thread.threadUrl, '_blank')
-    if (copied) {
-      toast('Draft copied — open the reply in Gmail and paste.', 'info')
-    } else if (text) {
-      toast('Could not copy draft. Open Gmail and paste manually.', 'error')
+    const recipient = mode === 'reply' ? extractAddress(latest?.from) : ''
+    if (!recipient) {
+      toast('No recipient found for this thread.', 'error')
+      return
+    }
+
+    const rawSubject = thread.subject || ''
+    const subject = mode === 'reply'
+      ? (/^re:/i.test(rawSubject) ? rawSubject : `Re: ${rawSubject}`.trim())
+      : (/^fwd:/i.test(rawSubject) ? rawSubject : `Fwd: ${rawSubject}`.trim())
+
+    // Build References chain from all known message ids (newest last).
+    const messageIds = thread.messages
+      .map((m) => m.messageIdHeader)
+      .filter((v): v is string => Boolean(v))
+    const references = messageIds.join(' ')
+    const inReplyTo = latest?.messageIdHeader
+
+    setSending(true)
+    try {
+      const result = await window.ipc.invoke('gmail:sendReply', {
+        threadId: thread.threadId,
+        to: recipient,
+        subject,
+        bodyHtml: html,
+        bodyText: text,
+        inReplyTo,
+        references: references || undefined,
+      })
+      if (result.error) {
+        toast(`Send failed: ${result.error}`, 'error')
+        return
+      }
+      toast('Sent.', 'success')
+      onClose()
+    } catch (err) {
+      toast(`Send failed: ${err instanceof Error ? err.message : String(err)}`, 'error')
+    } finally {
+      setSending(false)
     }
   }
 
@@ -666,10 +682,11 @@ function ComposeBox({
             type="button"
             className="gmail-send-button"
             onClick={() => { void sendInGmail() }}
-            title="Copy draft and open this thread in Gmail"
+            disabled={sending}
+            title="Send this reply via Gmail"
           >
-            <Send size={15} />
-            Send
+            {sending ? <LoaderIcon size={15} className="animate-spin" /> : <Send size={15} />}
+            {sending ? 'Sending…' : 'Send'}
           </button>
           <button
             type="button"
diff --git a/apps/x/packages/core/src/auth/providers.ts b/apps/x/packages/core/src/auth/providers.ts
index 52bd0ab5..8140055b 100644
--- a/apps/x/packages/core/src/auth/providers.ts
+++ b/apps/x/packages/core/src/auth/providers.ts
@@ -75,7 +75,7 @@ const providerConfigs: ProviderConfig = {
       mode: 'static',
     },
     scopes: [
-      'https://www.googleapis.com/auth/gmail.readonly',
+      'https://www.googleapis.com/auth/gmail.modify',
       'https://www.googleapis.com/auth/calendar.events.readonly',
       'https://www.googleapis.com/auth/drive.readonly',
     ],
diff --git a/apps/x/packages/core/src/knowledge/sync_gmail.ts b/apps/x/packages/core/src/knowledge/sync_gmail.ts
index 8057df86..e6ab9bad 100644
--- a/apps/x/packages/core/src/knowledge/sync_gmail.ts
+++ b/apps/x/packages/core/src/knowledge/sync_gmail.ts
@@ -26,7 +26,7 @@ const CACHE_DIR = path.join(WorkDir, 'inbox_lists');
     }
 })();
 const SYNC_INTERVAL_MS = 30 * 1000; // Check every 30 seconds
-const REQUIRED_SCOPE = 'https://www.googleapis.com/auth/gmail.readonly';
+const REQUIRED_SCOPE = 'https://www.googleapis.com/auth/gmail.modify';
 const MAX_THREADS_IN_DIGEST = 10;
 const RECENT_BACKFILL_INTERVAL_MS = 15 * 60 * 1000;
 const nhm = new NodeHtmlMarkdown();
@@ -114,6 +114,7 @@ export interface GmailThreadSnapshot {
             sizeBytes?: number;
             savedPath: string;
         }>;
+        messageIdHeader?: string;
     }>;
 }
 
@@ -1158,6 +1159,100 @@ async function performSync() {
     }
 }
 
+// --- Send Reply ---
+
+export interface SendReplyOptions {
+    threadId: string;
+    to: string;
+    subject: string;
+    bodyHtml: string;
+    bodyText: string;
+    inReplyTo?: string;
+    references?: string;
+}
+
+export interface SendReplyResult {
+    messageId?: string;
+    error?: string;
+}
+
+function encodeRfc2047(text: string): string {
+    // Only encode if non-ASCII chars present.
+    // eslint-disable-next-line no-control-regex
+    if (/^[\x00-\x7F]*$/.test(text)) return text;
+    return `=?UTF-8?B?${Buffer.from(text).toString('base64')}?=`;
+}
+
+export async function sendThreadReply(opts: SendReplyOptions): Promise<SendReplyResult> {
+    const auth = await GoogleClientFactory.getClient();
+    if (!auth) return { error: 'Gmail is not connected.' };
+
+    const gmailClient = google.gmail({ version: 'v1', auth });
+    const userEmail = await getUserEmail(auth);
+    if (!userEmail) return { error: 'Could not determine your Gmail address.' };
+
+    const boundary = `b_${Date.now()}_${Math.random().toString(36).slice(2, 10)}`;
+    const headers: string[] = [];
+    headers.push(`From: ${userEmail}`);
+    headers.push(`To: ${opts.to}`);
+    headers.push(`Subject: ${encodeRfc2047(opts.subject)}`);
+    if (opts.inReplyTo) headers.push(`In-Reply-To: ${opts.inReplyTo}`);
+    if (opts.references) headers.push(`References: ${opts.references}`);
+    headers.push('MIME-Version: 1.0');
+    headers.push(`Content-Type: multipart/alternative; boundary="${boundary}"`);
+
+    const parts: string[] = [];
+    parts.push(`--${boundary}`);
+    parts.push('Content-Type: text/plain; charset="UTF-8"');
+    parts.push('Content-Transfer-Encoding: 7bit');
+    parts.push('');
+    parts.push(opts.bodyText);
+    parts.push('');
+    parts.push(`--${boundary}`);
+    parts.push('Content-Type: text/html; charset="UTF-8"');
+    parts.push('Content-Transfer-Encoding: 7bit');
+    parts.push('');
+    parts.push(opts.bodyHtml);
+    parts.push('');
+    parts.push(`--${boundary}--`);
+
+    const message = `${headers.join('\r\n')}\r\n\r\n${parts.join('\r\n')}`;
+    const raw = Buffer.from(message)
+        .toString('base64')
+        .replace(/\+/g, '-')
+        .replace(/\//g, '_')
+        .replace(/=+$/, '');
+
+    try {
+        const res = await gmailClient.users.messages.send({
+            userId: 'me',
+            requestBody: { raw, threadId: opts.threadId },
+        });
+
+        // Clean up any Gmail-side drafts in this thread.
+        try {
+            const drafts = await gmailClient.users.drafts.list({ userId: 'me' });
+            const matching = (drafts.data.drafts || []).filter(
+                (d) => d.message?.threadId === opts.threadId && d.id
+            );
+            await Promise.all(
+                matching.map((d) =>
+                    gmailClient.users.drafts.delete({ userId: 'me', id: d.id! })
+                )
+            );
+        } catch (cleanupErr) {
+            console.warn('[Gmail] Draft cleanup after send failed:', cleanupErr);
+        }
+
+        // Wake the sync loop so the cache picks up the new message.
+        triggerSync();
+
+        return { messageId: res.data.id || undefined };
+    } catch (err) {
+        return { error: err instanceof Error ? err.message : String(err) };
+    }
+}
+
 export async function init() {
     console.log("Starting Gmail Sync (TS)...");
     console.log(`Will sync every ${SYNC_INTERVAL_MS / 1000} seconds.`);
diff --git a/apps/x/packages/shared/src/blocks.ts b/apps/x/packages/shared/src/blocks.ts
index ce8ce43c..69b331c4 100644
--- a/apps/x/packages/shared/src/blocks.ts
+++ b/apps/x/packages/shared/src/blocks.ts
@@ -123,6 +123,7 @@ export const GmailThreadMessageSchema = z.object({
   unread: z.boolean().optional(),
   bodyHeight: z.number().int().positive().optional(),
   attachments: z.array(GmailAttachmentSchema).optional(),
+  messageIdHeader: z.string().optional(),
 });
 
 export type GmailThreadMessage = z.infer<typeof GmailThreadMessageSchema>;
diff --git a/apps/x/packages/shared/src/ipc.ts b/apps/x/packages/shared/src/ipc.ts
index 37cf41e7..2a9e75c1 100644
--- a/apps/x/packages/shared/src/ipc.ts
+++ b/apps/x/packages/shared/src/ipc.ts
@@ -148,6 +148,21 @@ const ipcSchemas = {
     req: z.object({}),
     res: z.object({}),
   },
+  'gmail:sendReply': {
+    req: z.object({
+      threadId: z.string().min(1),
+      to: z.string().min(1),
+      subject: z.string(),
+      bodyHtml: z.string(),
+      bodyText: z.string(),
+      inReplyTo: z.string().optional(),
+      references: z.string().optional(),
+    }),
+    res: z.object({
+      messageId: z.string().optional(),
+      error: z.string().optional(),
+    }),
+  },
   'gmail:saveMessageHeight': {
     req: z.object({
       threadId: z.string().min(1),