Mailpit

Mailpit catches the email your applications send. Its SMTP server stores
every message, a web interface shows them (HTML, text, source, headers
and attachments) and a REST API lets automated tests read them. It also
offers message tagging, HTML and link checks, SMTP relaying and an
optional POP3 server.

Getting started

The service starts right after installation and listens on this machine
only: SMTP on 127.0.0.1:1025, the web interface and API on http://127.0.0.1:8025. Send a test message:

printf 'To: you@example.com\nSubject: Test\n\nHello\n' | mailpit sendmail

Settings

sudo snap set mailpit smtp-address=0.0.0.0:1025

sudo snap set mailpit http-address=0.0.0.0:8025

Other upstream settings, such as authentication, TLS, relaying and
message limits, go in /var/snap/mailpit/common/mailpit.env as MP_*
variables. Restart the service after editing it:

sudo snap restart mailpit.daemon

sendmail

mailpit.sendmail is a sendmail replacement that delivers to the service.

Captured mail is stored in /var/snap/mailpit/common. Updates come through
snap refresh; the upstream version check is disabled.