Ah the famous test@test.test email addresses we used to use in our test scripts to avoid sending email to anyone by accident. If we need to test the contents of the email then we use Mailhog these days. Can’t recommend it enough.
We have been successfully using https://github.com/axllent/mailpit
And not sure about this, but at least for docker, the included certificates can become outdated if not frequently rebuilt, and since Mailhog is software used when testing, being able to spin up a ready-to-use sandboxed instance is very useful.