# POST /email/reply

**Resource:** [Email](./email.md)  
**Scopes:** `email:send`  
**Write operation:** yes

Reply to an existing email thread. Default mode is "company" (uses configured provider). Use mode "personal" with sender_user_id for a user's Gmail.

## Parameters

| Name | In | Type | Required | Description |
|------|----|------|----------|-------------|
| `thread_id` | body | uuid | yes | Thread ID to reply to |
| `reply_html` | body | string | yes | Reply HTML body |
| `to_email` | body | string | yes | Recipient email |
| `to_name` | body | string | no | Recipient name |
| `cc` | body | string | no | CC recipients as comma-separated email addresses |
| `in_reply_to` | body | string | no | Message ID to reply to (for threading) |
| `mode` | body | string | no | Send mode: "company" (default) or "personal" |
| `sender_user_id` | body | uuid | no | User UUID whose Gmail to reply from (required when mode is "personal") |
| `from_email` | body | string | no | Send-as alias when mode is "personal". Must be a valid alias for the sender. Use GET /email/capabilities to see available aliases. |
| `attachments` | body | array | no | File attachments (Gmail only, max 25MB total). Array of objects with filename, mime_type, and content (base64-encoded file data). |

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