Aurinko Email API vs Fastmail API (JMAP)

Aurinko Email API

One REST interface covers message search with 17 query operators, drafts, sending, folders and delta sync across seven mailbox types, at $1.50 an active account a month and with send-only and read-only scopes. No status page, SLA, changelog, idempotency key on send or official SDK was found, and SOC 2 is not yet held.

Fastmail API (JMAP)

A mailbox API built on the open JMAP standard, with read-only tokens, six OAuth scopes and an MCP server that separates read, write and send access. Fastmail publishes no OpenAPI file, SDK, API changelog, request rate limit or SLA, and its customer terms forbid programmatically generated email to addresses outside the account.

Aurinko Email API

1. Use https://api.aurinko.io/v1. Several cURL examples in the docs print https:/api.aurinko.io with one slash, and one search example names the host asti.aurinko.io
2. Do not retry POST /v1/email/messages blindly after a timeout. There is no idempotency key, so check Sent mail with q=rfc822msgid: or by subject first
3. Call POST /v1/email/sync until ready is true, then page /v1/email/sync/updated with pageToken until a nextDeltaToken appears and store it
4. Check the omitted array on message lists. Full bodies come only from Google and Office 365, and other providers return a snippet
5. Request Mail.Read plus Mail.Send for read and send without modify rights. The docs example names Mail.ReadOnly, which is not in the scope list

Fastmail API (JMAP)

1. Fetch https://api.fastmail.com/jmap/session with Authorization: Bearer <token> first. It returns the API URL, account IDs and the request limits to stay under
2. Ask the owner for a read-only token unless the task writes. Sending needs both the Email and Email submission scopes
3. Request only the properties you need. Body text is not returned unless fetchTextBodyValues is set, and maxBodyValueBytes caps it
4. Sync with Email/changes from a stored state. On cannotCalculateChanges, fetch again from scratch
5. Do not send generated mail to outside recipients without the owner's review. The customer terms forbid it, and trial accounts stop at 120 messages a day