Choose Postmark if
- Deliverability is your number-one requirement and you only send transactional.
- You want Postmark's opinionated separation of transactional vs broadcast streams.
- Your users are humans and no AI agent is involved in the conversation.
Choose Loomal if
- Your agent actually needs to read replies and act on them.
- You want the agent to log into services (vault + TOTP) without a separate secrets store.
- You need per-agent isolation so revocation doesn't affect other deployments.
- You want native MCP tools instead of wrapping a REST client by hand.
Feature-by-feature
| Feature | Loomal | Postmark | Edge |
|---|---|---|---|
| Deliverability (transactional) | DKIM + SPF + DMARC aligned | Best-in-class, long track record | |
| Inbound routing | Inbox per identity, webhook native | Inbound address hooks | |
| Thread stitching | Automatic | Manual reconstruction | |
| LLM-ready body text | extractedText strips quotes + sigs | Raw HTML/text body | |
| Per-agent identity | One identity = inbox + vault + TOTP | Not a concept | |
| Credential vault | AES-256 per identity | None | |
| TOTP / 2FA codes | Built in | None | |
| Message streams (transactional vs broadcast) | Labels + stream analogue | First-class concept | |
| MCP server | First-party | None | |
| Delegation chain | Native | Not applicable |
Philosophy difference
Postmark has long argued that transactional and marketing email should be separated at the provider level. That philosophy shows up in the product: clear streams, strict deliverability discipline, tight API surface. It's an opinion we actually agree with.
Loomal adds a further separation: human email vs agent email. Agents send differently (more templated, higher volume bursts, different recipient patterns), need to receive (not just send), and need credentials and 2FA alongside the mailbox. Treating agents as a third kind of sender with its own primitive set is Loomal's core argument.
What breaks when you push Postmark into the agent role
You can do it. Postmark's inbound webhook handles receive; you can maintain thread state externally; you can layer a secrets manager alongside it. The cumulative integration cost is the problem, especially for small teams shipping multiple agents.
The sharper issue is revocation. If an agent is compromised and you need to pull every credential it touched, Postmark only gives you its email surface. You're still chasing the vault, the OAuth grants, the downstream API keys. Loomal's delegation chain makes this one operation.
FAQ
Is Loomal's deliverability as good as Postmark's?
For typical agent workloads, yes. Postmark's edge is in campaign-scale transactional volumes where reputation tuning matters most. If you're below that scale, you'll see comparable delivery rates.
Does Loomal have Message Streams?
We use labels to achieve similar separation — a 'transactional' label, a 'outreach' label, a custom label per workflow. It's less opinionated but gets to the same outcome.
Can I use both?
Yes. Some teams keep Postmark for human-facing transactional mail and use Loomal for AI agent mailboxes. They operate in separate domains and don't conflict.
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Last updated: 2026-04-15