You can have full-featured mailserver installed in couple minutes mostly waiting until script get job done. Whole package was designed with sane defaults to start quickly without knowing internals and without doing decisions which can break e-mail system.
Mail Server:
https://poste.io/
Demo:
https://demo.poste.io/admin/login#admin@poste.io;admin
Mail Server:
https://poste.io/
Demo:
https://demo.poste.io/admin/login#admin@poste.io;admin