Another alternative is using chromatic's Test::MockObject to simulate the mail server. Mocking allows you to unit test your mail generating component independently from the mail server, and you will be able to trap the output of your code to verify the contents of your mail.

This will not be enough, though, as you will need to test the component in combination with the mail server too. The unit tests will verify the interfaces between the two. I don't think mocking is the complete solution to your problem, but it will get you closer to your goal.

Good luck!

Update: Fixed som typos