# Attachments

Upload, attach, and download files on email messages.

## Upload flow

Outbound attachments use a two-step process:

1. **Upload** — POST a file to `/v1/attachments` as multipart form data. You get back an attachment ID.
2. **Attach** — Include the attachment ID(s) in the `attachments` array when sending a message via `POST /v1/mailboxes/:id/messages`.

**Inbound** attachments are extracted automatically by the JMAP poller: bytes are uploaded to R2, an `Attachment` row is linked to the inbound `Message`, and a fresh presigned `download_url` is included in every `message.received` webhook/SSE event. See [Inbound attachments](https://robotomail.com/docs/api/messages#inbound-attachments) for the schema, the size/count caps, and the inline image rewrite example.


## Downloading attachments

Fetch attachment metadata and a presigned download URL via `GET /v1/attachments/:id`. The presigned URL is valid for 24 hours and points directly to Cloudflare R2 storage. See the [Attachments API reference](https://robotomail.com/docs/api/attachments).


## Size limits

- Outbound: max file size per attachment **25 MB**; max total message size **40 MB** (Resend limit).
- Inbound: max file size per attachment **25 MB**; max **20 attachments** per inbound message. Over-cap parts are dropped and the message row is flagged with `attachmentsDropped: true`.
- Storage counts toward your account's storage quota


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