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What is simmail

simmail is simulated email for testing software that sends and reads mail.

Your app points its SMTP settings at simmail, the same way it would point them at a real provider. Every message lands in a mailbox inside simmail. On the other side are simulated people, called personas. They read your mail or ignore it, click its links, look up who sent it, make promises, file it as spam, and write back in character, on their own schedule.

simmail cannot send real mail. It has no relay and no outbound SMTP client. Mail addressed to anyone, at any domain, stays inside simmail.

What you can do with it

Section titled “What you can do with it”
  • Test sign-up and password-reset flows. Wait for the email your app sends, then pull out the one-time code or the magic link. See the wait API.
  • Test conversations. Send an offer to dana@harbor.test and get a reply that answers what you wrote. Dana remembers you next time. See People.
  • Test what goes wrong. Bounces, full mailboxes, greylisting, rate limits and dropped connections, with the codes real providers send. See Chaos and faults.
  • Check your mail’s health. Every message your app sends gets a spam score, a link check, a client-compatibility report and an accessibility report. See the health report.
  • Give an AI agent a mailbox. Agents connect over MCP and send, wait and read like any app. See Connect an AI agent.

How it fits together

Section titled “How it fits together”
PartWhat it does
SMTP and IMAPYour app sends over SMTP and reads over IMAP, with logins you create.
The HTTP APIEverything else: personas, the clock, waiting for mail, health reports, webhooks.
MCPThe same abilities as tools for AI agents.
The dashboardA web view of one universe: its mail, its people, what is about to happen.

Each customer’s work lives in one or more universes. A universe is a separate world with its own mail, logins, people, clock and settings. See Universes.

Getting an account

Section titled “Getting an account”

Sign up at www.simmail.dev. You get an organization, a first universe and its connection details. Plans set limits such as AI actions per month. See Accounts and billing.

Next steps

Section titled “Next steps”