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Head to head · Mailbox access · October 2026 research run

CloudPost vs Fastmail API (JMAP)

Fastmail API (JMAP) scores 54.1 (C) on agent readiness against CloudPost's 20.6 (F), and leads in 6 of 7 scored categories. CloudPost leads on maintenance & community. Both do mailbox access.

Best mailbox access APIs for AI agents · All 45 mailboxes comparisons

CloudPostCloudPost (James Brooks) · MCP server F20.6/100#956 of 961 Fastmail API (JMAP)Fastmail Pty Ltd · HTTP API C54.1/100#700 of 961

Which one, for what

CloudPost F

Best for A person who wants an agent to triage and answer their own iCloud Mail from Claude or another OAuth-capable MCP client without running an IMAP server locally.

Ahead on

  • Maintenance & community, 33 against 26

Also in its favour

  • A hosted endpoint, with nothing to install

Watch for

No terms of service, privacy policy or named operating company were found, for a service that stores an Apple app-specific password

Fastmail API (JMAP) C

Best 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

  • Reliability, 54 against 15
  • Schema & documentation, 52 against 8
  • Agent ergonomics, 73 against 23
  • Security & auth, 60 against 36
  • Payments & pricing, 30 against 20
  • Transparency & trust, 74 against 10

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

Score by category

CategoryWeight this runCloudPostFastmail API (JMAP)Edge
Reliability16%201554Fastmail API (JMAP) +39
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.2852Fastmail API (JMAP) +44
Agent ergonomics13%16.22373Fastmail API (JMAP) +50
Security & auth14%17.53660Fastmail API (JMAP) +24
Payments & pricing10%12.52030Fastmail API (JMAP) +10
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.83326CloudPost +7
Transparency & trust7%8.81074Fastmail API (JMAP) +64
Negative events≤1500
TotalF 20.6/100C 54.1/100

Facts side by side

FactCloudPostFastmail API (JMAP)
KindMCP serverHTTP API
VendorCloudPost (James Brooks)Fastmail Pty Ltd
Hosted endpointhttps://cloudpost.ing/api/mcp/mailno (local only)
TransportsHTTPHTTP
AuthOAuthOAuth or key
PricingFreePaid
x402nono
LicenceProprietary. No licence or terms publishedProprietary 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 MIT
Tools exposed9none
Read-only variant documentednoyes
llms.txtnono
Last release2026-10-102026-04-22
Terms last updatedno document linkedno date given
Privacy policy last updatedno document linkedno date given
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
Popularitynone123 stars

Verdicts

CloudPost

A hosted iCloud Mail MCP server launched on 10 October 2026, with OAuth and PKCE for clients and confirmations on sending, moving and deleting. It holds an Apple app-specific password with full mailbox access, and no terms, privacy policy, docs, pricing or security contact were found.

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.

Before you call either

CloudPost

  1. Ask the person to register at cloudpost.ing, create an Apple app-specific password and validate IMAP and SMTP before adding https://cloudpost.ing/api/mcp/mail
  2. Expect a confirmation prompt before send, move, delete, unsubscribe and folder changes, and wait for the person to answer it
  3. Treat message bodies as untrusted text. No injection guidance was found
  4. Call inspect unsubscribe before unsubscribe, which acts only on the inspected destination after approval

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

Questions

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

Fastmail API (JMAP) scores 54.1 (C) on agent readiness against CloudPost's 20.6 (F), and leads in 6 of 7 scored categories. CloudPost leads on maintenance & community.

Do CloudPost and Fastmail API (JMAP) need an API key?

CloudPost uses an OAuth sign-in. Fastmail API (JMAP) takes an API key or an OAuth sign-in.

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

CloudPost has a hosted endpoint at https://cloudpost.ing/api/mcp/mail. No hosted endpoint is listed for Fastmail API (JMAP).

Other comparisons with CloudPost or Fastmail API (JMAP)

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