# EmailEngine vs Fastmail API (JMAP) (slim)

> EmailEngine scores 71.4 (BB) on agent readiness against Fastmail API (JMAP)'s 54.1 (C), and leads in 6 of 7 scored categories. Both do mailbox read. Category scores, facts, verdicts and agent notes side by side.

- Full: https://www.anchorterminal.com/compare/emailengine-vs-fastmail.md (~2,200 tokens) · this version ~680 tokens · JSON https://www.anchorterminal.com/compare/emailengine-vs-fastmail.json · canonical https://www.anchorterminal.com/compare/emailengine-vs-fastmail
- Index: https://www.anchorterminal.com/llms.txt · API: https://www.anchorterminal.com/api/v1/index.json · Updated: 2026-10-09

EmailEngine scores 71.4 (BB) on agent readiness against Fastmail API (JMAP)'s 54.1 (C), and leads in 6 of 7 scored categories. Both do mailbox read.

- EmailEngine: BB 71.4, rank #123 of 842 · https://www.anchorterminal.com/tools/emailengine.min.md
- Fastmail API (JMAP): C 54.1, rank #620 of 842 · https://www.anchorterminal.com/tools/fastmail.min.md
- EmailEngine, good for A team that must keep mailbox access on its own infrastructure, has many mailboxes across Gmail, Microsoft 365 and IMAP, and can run a server and Redis. Ahead on Reliability, 79 against 54; Schema & documentation, 91 against 52; Agent ergonomics, 80 against 73; Security & auth, 71 against 60; Payments & pricing, 40 against 30; Maintenance & community, 81 against 26. Also Agent-ready, a grade of BB or better.
- Fastmail API (JMAP), 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. Also No incidents deducted, where EmailEngine loses 3 points for them.

| Category | EmailEngine | Fastmail API (JMAP) |
| --- | --- | --- |
| Reliability (16%) | 79 | 54 |
| Performance (10%) | pending | pending |
| Schema & documentation (13%) | 91 | 52 |
| Agent ergonomics (13%) | 80 | 73 |
| Security & auth (14%) | 71 | 60 |
| Payments & pricing (10%) | 40 | 30 |
| Task success (10%) | pending | pending |
| Maintenance & community (7%) | 81 | 26 |
| Transparency & trust (7%) | 72 | 74 |

| Fact (where they differ) | EmailEngine | Fastmail API (JMAP) |
| --- | --- | --- |
| Vendor | Postal Systems OÜ | Fastmail Pty Ltd |
| Auth | API key | OAuth or key |
| Licence | Source available under the EmailEngine licence agreement, version 2.1 of 17 October 2023. Not open source. The PHP SDK is MIT | Proprietary 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 |
| Read-only variant documented | no | yes |
| llms.txt | yes | no |
| Last release | 2026-10-05 | 2026-04-22 |
| Terms restrict automated access | yes | not found in the text |
| Terms restrict benchmarking | not found in the text | yes |
| Terms or service can change without notice | yes | not found in the text |
| Popularity | 2.2k stars, 388 npm/wk | 123 stars |