---
title: "Send Message"
method: POST
path: "/api/v1/mail/mailboxes/{email_address}/messages"
tags: ["Messages"]
---

# Send Message

`POST /api/v1/mail/mailboxes/{email_address}/messages`

## Path parameters

- `email_address` string, required

## Headers

- `Idempotency-Key` string, nullable

## Request body

- MessageSend
  - `recipients` Recipients, required
    - `to` string[], nullable
    - `cc` string[], nullable
    - `bcc` string[], nullable
  - `subject` string, required
  - `body_text` string, nullable
  - `body_html` string, nullable
  - `thread_id` string, uuid, nullable — Attach this message to an existing conversation. Preferred over in_reply_to_message_id when replying; pass the thread_id returned by the list/get endpoints.
  - `in_reply_to_message_id` string, nullable — Message-ID of the email being replied to
  - `attachments` AttachmentUpload[], nullable
    - `filename` string, required
    - `content_type` string, required — MIME type, e.g. image/jpeg
    - `content_base64` string, required — Base64-encoded file content
    - `content_id` string, nullable — Mark this part as an inline image referenced from body_html as cid:<content_id> (e.g. <img src="cid:chart1">). Surrounding angle brackets are optional. Omit for a normal attachment.
  - `staged_attachments` StagedAttachmentReference[], nullable
    - `media_handle` string, uuid, required
    - `filename` string, required
    - `content_hash` string, required
    - `content_type` string, required
    - `content_id` string, nullable
  - `reply_to` string, email, nullable — Optional Reply-To address. If set, recipients' mail clients route replies here instead of the From mailbox.
  - `track_opens` boolean — Embed an open-tracking pixel in the HTML body. Requires body_html; a send with track_opens and no HTML body is rejected with 422. Opens surface as first_opened_at/open_count on the message. Note: tracking pixels can raise spam scores.

## Response `201`

Successful Response

- MessageResponse
  - `id` string, uuid, required
  - `mailbox_id` string, uuid, required
  - `thread_id` string, uuid, nullable, required
  - `message_id` string, nullable
  - `from_address` string, required
  - `to_addresses` string[], required
  - `cc_addresses` string[], nullable, required
  - `subject` string, nullable, required
  - `snippet` string, nullable, required
  - `direction` 'inbound' | 'outbound', required
  - `status` 'queued' | 'sent' | 'delivered' | 'bounced' | 'failed' | 'received' | 'deleted', required
  - `is_read` boolean, required
  - `is_starred` boolean, required
  - `has_attachments` boolean, required
  - `reply_to` string, nullable
  - `first_opened_at` string, date-time, nullable
  - `open_count` integer
  - `created_at` string, date-time, required
  - `updated_at` string, date-time, nullable
  - `sending_domain_warning` string, nullable
  - `import_job_id` string, uuid, nullable

## Other responses

- `422` — Validation Error
- `4XX` — Client error with Support Agent information.
- `5XX` — Server error with Support Agent information.

---

[API](https://skmtc.dev/inkbox/apis/inkbox-api.md) · [All operations](https://skmtc.dev/inkbox/apis/inkbox-api/llms.txt) · [OpenAPI document](https://skmtc-service-production.skmtc.workers.dev/v1/apis/inkbox/inkbox-api/revisions/31f357e7e6f8/schema)