- Fast SMTP processing & storing - approximately 70-100 emails per second depending on CPU, network speed & email size, easily handling tens of thousands of emails
- SMTP relaying / message release - relay messages via a different SMTP server including an optional allowlist of accepted recipients ([see wiki](https://github.com/axllent/mailpit/wiki/SMTP-relay))
- Optional SMTP with STARTTLS & SMTP authentication, including an "accept anything" mode ([see wiki](https://github.com/axllent/mailpit/wiki/SMTP-with-STARTTLS-and-authentication))
Static binaries can always be found on the [releases](https://github.com/axllent/mailpit/releases/latest). The `mailpit` binary can extracted and copied to your `$PATH`, or simply run as `./mailpit`.
Mailpit's SMTP server (by default on port 1025), so you will likely need to configure your sending application to deliver mail via that port. A common MTA (Mail Transfer Agent) that delivers system emails to a SMTP server is `sendmail`, used by many applications including PHP. Mailpit can also act as substitute for sendmail. For instructions of how to set this up, please refer to the [sendmail documentation](https://github.com/axllent/mailpit/wiki/Configuring-sendmail).
I had been using MailHog for a few years to intercept and test emails, but experienced a number of severe performance issues. Many of the frontend and Go libraries are very out of date, and the project [is no longer maintained](https://github.com/mailhog/MailHog/issues/442#issuecomment-1493415258).
Initially I tried to upgrade a fork of MailHog (the UI, the HTTP server and the API), but discovered that it is (with all due respect to its authors) far too complex. I found it over-engineered (split over 9 separate projects), and performs very poorly when dealing with large amounts of emails or emails with attachments (a single email with a 3MB attachment can take over a minute to ingest). Finally the API transmits a lot of duplicate & irrelevant data on every browser request, all without any HTTP compression.
