Reply to Email

Scope: mail:send

Reply to an existing email. The reply is automatically threaded.

Request

import { Mailgent } from "@mailgent/sdk";

const mailgent = new Mailgent({ apiKey: process.env.MAILGENT_API_KEY! });
const reply = await mailgent.mail.reply("<msg-id@gmail.com>", {
  text: "Thanks for your question! Here's the answer...",
});

import os
from mailgent import Mailgent

mailgent = Mailgent(api_key=os.environ["MAILGENT_API_KEY"])
reply = mailgent.mail.reply(
    "<msg-id@gmail.com>",
    text="Thanks for your question! Here's the answer...",
)

mailgent mail reply '<msg-id@gmail.com>' \
  --text "Thanks for your question! Here's the answer..."

Pass --html for an HTML body. Quote the messageId — it contains <>@.

mail.reply(message_id, text=..., html?)

Available through @mailgent/mcp — see MCP setup.

curl -X POST https://api.mailgent.dev/v0/messages/%3Cmsg-id%40gmail.com%3E/reply \
  -H "Authorization: Bearer loid-your-api-key" \
  -H "Content-Type: application/json" \
  -d '{"text":"Thanks! Here is the info you requested."}'

Body

{
  "text": "Thanks for your question! Here's the answer...",
  "html": "<p>Optional HTML reply</p>"
}

Field	Type	Required	Description
`text`	`string`	Yes	Plain text reply
`html`	`string`	No	HTML reply
`attachments`	`Attachment[]`	No	See Attachments

Response — 201 Created

{
  "messageId": "<new-uuid@mailgent.dev>",
  "threadId": "thd_f8e2a1c4d7b90e3f",
  "inboxId": "agent-x8k2m@mailgent.dev",
  "from": ["agent-x8k2m@mailgent.dev"],
  "to": ["sender@example.com"],
  "cc": [],
  "subject": "Re: Question about pricing",
  "text": "Thanks for your question! Here's the answer...",
  "extractedText": "Thanks for your question! Here's the answer...",
  "labels": ["sent"],
  "createdAt": "2026-03-28T14:30:00.000Z"
}

Errors

Status	Code	Description
`404`	`not_found`	Original message not found
`429`	`quota_exceeded`	Daily send limit reached (50/day)

Threading

Subject prefixed with Re: automatically
In-Reply-To header set to the original messageId
References header includes full chain
Same threadId as the original

Request

Body

Response — 201 Created

Errors

Threading

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