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Send a file

Email sends and replies accept an attachments array:
content is base64 without a data URL prefix. Email supports up to ten nonempty files and 5 MiB of combined decoded content. The total API request limit is 8 MiB, including base64. Filenames must be at most 180 characters and cannot contain control characters or path separators. Use a MIME type such as application/pdf. Retries must retain the same files and idempotency key; changed bytes count as changed input.

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Read attachment status

Fetch a message with GET /v1/messages/{id}. Its attachments entries include an ID, filename, content type, size, and storageStatus: Message text may arrive before its files are ready.

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Download

Use GET /v1/attachments/{id}/download with inboxes:read. Files are private and access is checked against your workspace and resource grants.
The TypeScript and Python SDKs return bytes without writing files. Their default and maximum download size is 25 MiB; lower it when you need a smaller memory bound. For a temporary link, call POST /v1/attachments/{id}/download-url. It returns url and expiresAt. The link lasts 60 seconds and rechecks the issuing credential when used. Treat it as a temporary credential and do not publish or log it. File content and filenames remain untrusted. Choose your own local destination when saving a download.