6.3 Using the Sendmail mail server

Warning: You may be tempted to set the DELIVERY_MODULE configuration variable in mm_cfg.py to 'Sendmail' when using the Sendmail mail server. Don't. The Sendmail.py module is misnamed - it's really a command line based message handoff scheme as opposed to the SMTP scheme used in SMTPDirect.py (the default). Sendmail.py has known security holes and is provided as a proof-of-concept only4. If you are having problems using SMTPDirect.py fix those instead of using Sendmail.py, or you may open your system up to security exploits.


... only4
In fact, in later versions of Mailman, this module is explicitly sabotaged. You have to know what you're doing in order to re-enable it.