Why We Built Postbox When AgentMail Exists

I have a healthy respect for AgentMail. The Show HN thread, the YC fundraise, the polish of the dashboard — they've executed well. They're a useful product.

So why build Postbox?

Same shape, different stack

AgentMail is a closed-source SaaS. Postbox is Apache-2.0 SDK + open-source MCP server + self-hostable backend. If you want self-host or you want the SDK source, you couldn't have AgentMail; you can have Postbox.

Self-hostable mattered to us

The Ujex bet is that agent infra should look like Firebase: one project, your data, replaceable boundaries. AgentMail breaks that — it's an outside vendor with its own auth and billing. We wanted everything (email, memory, ingress, budgets, mobile, audit) to share one project, one Firestore, one auth, one bill.

Prompt-injection scoring built in

Email is the most public input an agent will ever see. We score every inbound message (heuristic regex + Gemini fallback). AgentMail does some scoring; ours is exposed in the API + audit log so the agent can route high-PI messages to a human approval queue. This was a non-negotiable for us.

Mobile approve-before-send

Outbound email is irreversible. We added mobile approve-before-send as a first-class field on postbox.send: require_approval=true queues the message, fires FCM push, blocks until human approves. AgentMail doesn't have this; you'd build it on top.

Same auth as the rest of the agent stack

Ujex agents have device keys with scopes. postbox:send is a scope. The same key that authenticates a memory call authenticates a send call. AgentMail has its own API keys — fine, but a separate concept.

Replaceable boundary

If Ujex Postbox isn't enough for your scale, swap to AgentMail. The interface is similar enough that the agent code barely changes. The Postbox subsystem sits behind a module boundary; we proved this when we swapped Postmark → Brevo in one day.

What AgentMail is better at

Polish. The dashboard is more refined. Customer support is more responsive (they're a SaaS company; we're a research project that became a product). Deliverability at scale is better-warmed.

What we're better at

Self-hostable. Apache-2.0 SDK. Prompt-injection scoring as a first-class output. Mobile approve-before-send. Same project as memory + audit + ingress.

Both should exist

For most teams who want zero ops, AgentMail is the right answer. For teams who want ownership, Apache-2.0, and integration with the rest of an agent stack, we exist for that. Pick what fits.