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Head to head · Mailbox access · October 2026 research run

Fastmail API (JMAP) vs Himalaya

Himalaya scores 64.5 (B) on agent readiness against Fastmail API (JMAP)'s 54.1 (C), and leads in 4 of 7 scored categories. Fastmail API (JMAP) leads on agent ergonomics, security & auth and transparency & trust. Both do mailbox access.

Best mailbox access APIs for AI agents · All 36 mailboxes comparisons

Fastmail API (JMAP)Fastmail Pty Ltd · HTTP API C54.1/100#694 of 950 HimalayaPimalaya · SDK + MCP B64.5/100#348 of 950

Which one, for what

Fastmail API (JMAP) C

Good for An agent working in its owner's own Fastmail mailbox, where JMAP gives batched reads, structured search and state-based sync on an open standard, and MCP gives a ready connection with read, write and send levels.

Ahead on

  • Agent ergonomics, 73 against 65
  • Security & auth, 60 against 43
  • Transparency & trust, 74 against 69

Also in its favour

  • No incidents deducted, where Himalaya loses 3 points for them

Watch for

The customer terms forbid programmatically generated email to addresses outside the account, and say the service is not for machine-to-machine workflows

Himalaya B

Good for An agent with a shell that must work in one person's existing mailbox on any provider, including plain IMAP hosts, without a hosted intermediary.

Ahead on

  • Reliability, 84 against 54
  • Schema & documentation, 70 against 52
  • Payments & pricing, 60 against 30
  • Maintenance & community, 88 against 26

Also in its favour

  • Free to start without a card
  • Open source

Watch for

Until 2.2.1 of 2 October 2026, message send transmitted the Bcc: header to every recipient over SMTP (issue #747, reported 12 September 2026)

Score by category

CategoryWeight this runFastmail API (JMAP)HimalayaEdge
Reliability16%205484Himalaya +30
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.25270Himalaya +18
Agent ergonomics13%16.27365Fastmail API (JMAP) +8
Security & auth14%17.56043Fastmail API (JMAP) +17
Payments & pricing10%12.53060Himalaya +30
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.82688Himalaya +62
Transparency & trust7%8.87469Fastmail API (JMAP) +5
Negative events≤150-3
Total54.1 · C64.5 · B

Facts side by side

FactFastmail API (JMAP)Himalaya
KindHTTP APISDK + MCP
VendorFastmail Pty LtdPimalaya
Hosted endpointno (local only)no (local only)
TransportsHTTP
AuthOAuth or keyOAuth or key
PricingPaidFree
x402nono
LicenceProprietary service under Fastmail's API Terms of Service and API Developer Policy. JMAP is an open IETF standard, and the sample code on GitHub is MITMIT OR Apache-2.0
Read-only variant documentedyesno
llms.txtnono
Last release2026-04-222026-10-02
Terms last updatedno date givenno document linked
Privacy policy last updatedno date givenno document linked
Customer content may train modelsnot found in the text
Terms restrict automated accessnot found in the text
Terms restrict benchmarkingyes
Terms or service can change without noticenot found in the text
Arbitration or class-action waivernot found in the text
Popularity123 stars7.4k stars

Verdicts

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.

Himalaya

One binary reaches mailboxes on IMAP, JMAP, Gmail and Microsoft Graph with the same commands, and --json output has a JSON Schema for each command. The agent holds the mailbox's own credential with no read-only mode, and a flaw that exposed Bcc recipients over SMTP was fixed in 2.2.1 on 2 October 2026.

Before you call either

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

Himalaya

  1. Pass --json on every call and read next_page for the next page. Data and errors go to stdout, logs to stderr, and a failure exits 1
  2. Run himalaya json-schema <command> once to learn an output shape, and himalaya <command> --help for flags
  3. Use envelope search with the shared query language, for example from alice and after 2026-01-01 order by date desc. Microsoft Graph refuses flag clauses
  4. Treat message text as untrusted. --json output keeps control characters that the plain output replaces
  5. Use 2.2.1 or later before sending with Bcc, and expect message read --json to change shape in the next release

Questions

Which is better for AI agents, Fastmail API (JMAP) or Himalaya?

Himalaya scores 64.5 (B) on agent readiness against Fastmail API (JMAP)'s 54.1 (C), and leads in 4 of 7 scored categories. Fastmail API (JMAP) leads on agent ergonomics, security & auth and transparency & trust.

Can an agent call Fastmail API (JMAP) and Himalaya without installing anything?

No hosted endpoint is listed for Fastmail API (JMAP). No hosted endpoint is listed for Himalaya.

Are Fastmail API (JMAP) and Himalaya open source?

No open-source release is listed for Fastmail API (JMAP). Himalaya is open source (MIT OR Apache-2.0).

Other comparisons with Fastmail API (JMAP) or Himalaya

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