mails.ai Agent Email vs Postfleet

mails.ai Agent Email

Per-agent addresses with scoped, agent-bound keys, an OpenAPI spec and a prompt-injection score on every inbound message. The operator is unnamed, the vendor calls itself pre-launch, and the status page shows 98.49 per cent API uptime over 90 days with no incident reports.

Postfleet

Agent mailboxes over REST, webhooks and a 16-tool MCP server, with mailbox-bound keys, required idempotency keys on MCP sends, server-side approval and documented screening that keeps raw mail out of MCP reads. The screening is the vendor's claim, untested by us. Under four months old, it names no operator and has no status page, changelog or security contact.

mails.ai Agent Email

1. Use an mk_test_ key until the flow works. Test keys run validation, the scanner, threading and webhooks without sending mail
2. Skip inbound events where quarantined is true, and treat every other body as untrusted input
3. Send an Idempotency-Key header on POST /v1/messages so a retried send doesn't go out twice
4. Mint a key with only the scopes the task needs, bound to one agent with agent_id
5. Expect 422 cold_email_prohibited for unsolicited outreach. Read the error code rather than retrying

Postfleet

1. Check comprehension.status before acting; skipped_injection_risk mail still arrives as cleaned text and must be handled as untrusted data.
2. Treat a 202 pending_approval from send_email, reply_email or send_draft as success and never retry it; follow up with list_drafts.
3. Reuse the same client_id when retrying a send, and use a new one after a terminal 402, 403 hold or permanent 400.
4. Call list_mailboxes before create_mailbox; each create makes another mailbox and retries are not idempotent.
5. Give a reading agent a mailbox-bound key with can_send false, and keep the account-wide key outside the worker.