AgentMail Alternatives: 5 I Actually Tested
For "drop-in replace AgentMail's API shape" — Ujex Postbox is the closest. For "connect to existing Gmail" — Nylas. For "I'll build it myself on Mailgun" — works, but you're building per-agent inbox logic from scratch. ClawNet is a smaller player, worth a look.
I built five small test agents — same task (read an email, classify it, reply or escalate) — on five providers. Here's what I learned.
The test
An agent receives an email at support@my-test-domain.dev. If it looks like a feature request, it replies with "thanks, logged." If it looks urgent, it forwards to a human. Otherwise, it ignores. Goal: minimum code, maximum coverage of the provider's surface.
Provider 1: Nylas
Setup time: 25 minutes (OAuth dance, API key, one webhook URL). Code: ~80 lines. Surprise: Nylas wants OAuth even for testing — there's a sandbox flow but it's the same shape. Verdict: Best when your agent uses a real human's existing inbox. Wrong tool if you want a fresh per-agent address.
Provider 2: Mailgun + custom inbox layer
Setup time: 90 minutes (DNS, MX, route config, then write the per-agent layer). Code: ~250 lines (the per-agent layer is most of it). Surprise: The Mailgun route concept is elegant but it's per-route, not per-agent — I had to write a router that maps inbound mail to agents based on the local part. Verdict: Mature, fast, no surprises if you've used Mailgun before. Builds up to good if you have time.
Provider 3: Composio Gmail MCP
Setup time: 15 minutes (MCP config, OAuth). Code: ~50 lines. Surprise: Composio's tool wrapper does the right things for Claude Code / Cursor — invocation feels native. Verdict: Right for "agent uses my Gmail" through MCP. Same OAuth-shape as Nylas, narrower scope (Gmail only).
Provider 4: Self-host Postfix + OpenDKIM + Brevo
Setup time: 4 hours, mostly Hetzner port-25 unblock ticket. Code: ~150 lines (parsing webhook, inbox routing, outbound queue). Surprise: Brevo's free tier (300/day) is perfectly adequate for testing; the DKIM ap1 selector shows "neutral" in Gmail because Brevo modifies bodies — harmless but cosmetically noisy. Verdict: Real ops work, but if you want a stack you understand end-to-end and don't pay vendor margin, this is right.
Provider 5: Ujex Postbox
Setup time: 10 minutes (free-tier signup, one API call to create inbox). Code: ~30 lines. Surprise: Prompt-injection score on every inbound message — caught a deliberately-bad test message I sent to verify. Verdict: The agent-native shape AgentMail has, plus prompt-injection scoring + mobile approval + self-host option. Less polished than AgentMail in some places (e.g. the dashboard); the SDK + MCP server are solid.
Honorable mention: ClawNet
ClawNet launched late January and got attention. Smaller player; the agent-email category triples in user count any time AgentMail does (per AgentMail's TechCrunch profile). Worth tracking.
Side-by-side
| Nylas | Mailgun | Composio | Self-host | Ujex | |
|---|---|---|---|---|---|
| Setup time | 25min | 90min | 15min | 4h | 10min |
| Code lines | 80 | 250 | 50 | 150 | 30 |
| Per-agent inbox | ✗ | Build | ✗ | Build | ✓ |
| PI scoring | ✗ | Build | ✗ | Build | ✓ |
| Self-hostable | ✗ | Hybrid | ✗ | ✓ | ✓ |
Honest recommendation
If AgentMail's pricing is fine for you, AgentMail is honestly the easiest. If you want self-host or Apache-2.0 SDK, Ujex Postbox. If you want to be in the user's existing inbox, Nylas. The other three are right for narrower cases.
FAQ
How does Ujex's prompt-injection scoring actually work?
Heuristic regex pass first (cheap, catches obvious patterns). For ambiguous cases, falls back to Gemini 1.5 Flash for a structured score. Surfaced as piScore on the message document. Detailed in the Postbox subsystem docs.
Can I run AgentMail and Ujex side by side?
Yes — different MX records, different domains. We don't recommend it (operational complexity) but it's possible.
What about Postmark for agent inboxes?
Postmark's inbound stream is excellent for parsing. Per-agent inbox creation isn't their model — you'd build it on top, similar to Mailgun.