Fakemail provides a fake SMTP server for use in developing applications which rely on sending email. This works especially well for clients like Flask-Mail which do not have a "debug" mode to just print the mail to stdout.
The provided Procfile
demonstrates how to run the server - in this particular case if you set your application to send to $MAIL_PORT
this process will follow suit if it is set, and otherwise will connect on port 4467 (as used in the inbox.py samples.)
Fakemail depends on Kenneth Reitz's Inbox.py, but has no other dependencies.