Where they overlap
Both send DKIM-signed mail from your domain, both can receive, both publish an MCP server. Postmark's inbound webhook and message search give you parsed JSON and 45 days of retention.
Where Innmail is different
Innmail stores mail per agent, in threads, for as long as the inbox exists, and lets the agent reply in the same thread. Webhooks are HMAC-signed with retries and dedupe ids. Policies hold risky sends for a person, and inbound security can hold suspicious mail before the agent reads it. Postmark authenticates webhooks with Basic auth and has no approval or agent concept.
When Postmark fits better
For application email where inbox placement is the whole job, Postmark's reputation and message streams are hard to beat. If your agent just needs to send notifications, that is enough.
Innmail and Postmark at a glance
| Innmail | Postmark | |
|---|---|---|
| Inbox per agent | One API call creates a real inbox per agent | No per-agent inboxes |
| Receiving and threads | Receives, stores and threads replies; read them over the API | Inbound parse webhook plus a 45-day message search; no threads |
| Human approval | Policies hold risky outbound mail for a person to approve; no key can approve | No |
| Inbound security | Checks for spoofing, lookalike domains, pressure language and prompt injection; can hold mail before the agent reads it | SpamAssassin score on inbound mail |
| Events | Signed webhooks with retries, an SSE stream and a 30-day event log | Webhooks authenticated with Basic auth, not signatures |
| MCP and SDKs | MCP server, OpenAPI 3.1, SDKs for TypeScript, Python and Go, and a CLI | Official MCP server for sending and stats |
| Custom domains | Your own domain with DKIM, verified from the UI; unlimited inboxes on it | Yes |
| Free tier | Free beta: 3 @innmail.app inboxes and 100 outside recipients a day per workspace | Free: 100 emails a month; inbound needs the Pro plan from $16.50 a month |
Based on each product's public description as of 2026. Check Postmark's site for current details.
Frequently asked questions
Does Innmail do inbound parsing?
Yes, and it keeps the result: each inbound message is stored with headers, extracted reply text, attachments and the raw source, and routed to the right agent inbox.
Is Innmail's inbound free?
Receiving is included in the free beta. Postmark's inbound requires its Pro plan.
What does it cost?
Nothing during the private beta: 3 @innmail.app inboxes and 100 outside recipients a day per workspace, unlimited inboxes on a domain you verify. Mail between your own agents is not counted.
Give every AI agent its own inbox.
A real @innmail.app address in one API call, or one on your own domain. Free in the private beta, no Gmail to connect.
Request beta access