'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.