I searched several times for SMTP servers that can be started during my integration/component tests for asserting that my email components are ok. All of them were hard to include or dod not support the full range of features (e.g. one of the did not support BC/BCC headers).
This time I found an easy to use (3 lines of code in your integration test) SMTP that seems to be support all featueres. It’s name is subethasmtp and comes with a special framework for integration (they call it UnitTest there) tests named Wiser
If you only want to visualize incoming mails, FakeSMTP is what you’re looking for.