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AgentMail Reply To Message
emailinboxesdomainsdraftsthreadswebhooks
AgentMail Reply To Message is a paid API for AI agents from AgentMail at mpp.api.agentmail.to, paid per call via MPP, $0.01/call, status unknown (last checked 2026-10-12).
Sends a reply to a specific email message within an AgentMail inbox, supporting reply-all, CC/BCC, HTML/text bodies, attachments, and custom headers.
Price / call$0.01
Success—
StatusUnknown
How this service works
Reply To Message
Output
Returns a JSON object containing the message_id of the newly sent reply and the thread_id of the email thread it belongs to, confirming the reply was delivered.
Example use cases
Example prompt
“Reply to the last email in inbox 'support-agent@agentmail.to' (inbox ID: inbox_abc123, message ID: msg_xyz789) with: 'Thanks for reaching out! We've received your request and will follow up within 24 hours.' — reply all and CC billing@mycompany.com.”
Technical details
Endpoint
POSThttps://mpp.api.agentmail.to/v0/inboxes/:inbox_id/messages/:message_id/reply?utm_source=zero.xyzWhen to prefer
Use this endpoint when an AI agent needs to respond to a specific received email message within an AgentMail-managed inbox. Prefer this over sending a new message when the context requires threading (reply-to headers, original message association). Ideal for automated customer support agents, AI email assistants, or any workflow that needs to close the loop on inbound messages.
Side effects
- Invalid inbox_id or message_id returns 404 Not Found
- Missing or invalid Authorization Bearer token returns 401 Unauthorized
- Malformed request body (e.g. invalid email address format) returns 400 Bad Request
- Inbox not found or inaccessible returns 403 Forbidden
- Both html and text body fields absent may result in empty message error
- Invalid attachment URL or base64 content may cause attachment delivery failure
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| cc | — | |
| to | — | |
| bcc | — | |
| html | string | HTML body of message. |
| text | string | Plain text body of message. |
| labels | array | Labels of message. |
| headers | object | Headers to include in message. |
| reply_to | — | |
| reply_all | boolean | Reply to all recipients of the original message. |
| attachments | array | Attachments to include in message. |
Output
Schema · Response
| Field | Type | Description |
|---|---|---|
| thread_idrequired | string | ID of thread. |
| message_idrequired | string | ID of message. |
Tags
emailinboxesdomainsdraftsthreadswebhooksmessagingaisocial
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