/usr/bin/msmtpd

Usage: msmtpd [option...]
Options:
  --version       print version
  --help          print help
  --inetd         start single SMTP session on stdin/stdout
  --interface=ip  listen on ip instead of 127.0.0.1
  --port=number   listen on port number instead of 25
  --log=none|syslog|FILE  do not log anything (default)
                  or log to syslog or log to the given file
  --command=cmd   pipe mails to cmd instead of /usr/bin/msmtp -f %F --
  --auth=user[,passwordeval] require authentication with this user name;
                  the password will be retrieved from the given
                  passwordeval command or, if none is given, from
                  the key ring or, if that fails, from a prompt.