Run our own email (IMAP/POP3/SMTP) server for automated tests run on lizard

Originally created by @intrigeri on #12277 (Redmine)

See https://gitlab.tails.boum.org/tails/tails/-/issues/11890#note_49500 and https://gitlab.tails.boum.org/tails/tails/-/issues/11890#note_49503 for more detailed specs.

Feature Branch: test/11890-local-email-server

Related issues

• Related to tails/tails#11890