message/post_reply
Tool: act
Send a reply in an existing message thread.
Sends an email reply to a received message identified by its email messageId (the Message-ID header value). Supports quoting the original, CC/BCC, sender override, and personalization. Attachments are sent in-memory only and not stored.
This sends a real reply email — requires
confirm_send: truein arguments (the call is rejected withMCP_CONFIRMATION_REQUIREDwithout it). Consent must be fresh and specific to this reply: right before calling, tell the user what will be sent and to whom, and get their explicit yes. A general or earlier "go ahead" does NOT satisfy this — "yes, fix it" / "get this running" from earlier in the conversation does not count, and neither does the user merely asking how to reply or what's needed. Only setconfirm_send: trueif you have just asked the user to confirm THIS reply and they agreed in this exact context. When in doubt, ask first.
Arguments
| name | type | req | notes |
|---|---|---|---|
| confirm_send | boolean | ✓ | Required to actually send — set true only after your user gave a fresh, specific yes to this reply (a general earlier go-ahead doesn't count) |
Body
| field | type | req | constraints | description |
|---|---|---|---|---|
| messageId | string | ✓ | Message-ID header value of the received message to reply to. | |
| subject | string | – | ≤4000 chars | Reply subject. Defaults to original subject if omitted. |
| body | string | – | HTML reply body. Personalization is applied to it, but which variable names this operation accepts has not been verified — the vocabulary in personalization-variables is confirmed for campaign and followup content only. Literal text is always safe here. | |
| sendAsReply | boolean | – | default false | If true, appends the original message as a quoted block. |
| fromEmail | string | – | Sender override; must be a configured sender in the organization. Defaults to the original message's sender. | |
| replyToEmail | string | – | ≤128 chars | Prospect email to reply to. Defaults to the thread prospect's email if omitted. |
| ccEmails | string | – | Comma-separated CC addresses. | |
| bccEmails | string | – | Comma-separated BCC addresses. | |
| attachments | array | – | In-memory attachments (not persisted). | |
| attachments[].fileName | string | – | ||
| attachments[].contentType | string | – | ||
| attachments[].contentBase64 | string | – | Base64-encoded file content. |
Response
200 — {ok:true} acknowledgement.
Errors: 400, 401, 406, 409, 415, 422, 429, 500 — shared schema: schemas/errors.
Invoke
Call act with name: "message/post_reply".