ZMailer is an internet message transfer agent. It is intended for gateways or mail servers or other large site environments that have extreme demands on the abilities of the mailer. It was motivated by the problems of the Sendmail design in such situations. It is intended and designed as a multi-protocol mailer. The only protocol supported in this distribution is RFC822 (and variations).
asceticsmtp.py is a very minimal "ascetic" SMTP relay-only mail transport agent. It's intended to be used in conjunction with the mutt mail client to provide SMTP mail transport services. It accepts a mail stream on standard input with recipients specified on the command-line, and forwards the message to a given mailhub. SMTP authentication and SSL transport layer security is supported for recent enough Python libraries.
The deepOfix Mail Server makes it possible for organizations with minimal technical expertise to have robust server infrastructure. deepOfix offers unprecented ease of use, doesn't require prior GNU/Linux experience and is backed by a full-time development and support team. deepOfix features LDAP-based directory services for user account management, email delivery, distribution lists, and addressbooks. It also includes built in tools for spam and virus control, webmail, and fetching email.
dialin-spammer-block can be used to detect and block dialin clients that try to send send spam over your mailserver. A spammer is detected by watching the mailserver logfile and counting the mails sent by each dialin client. If a client exceeds the limit of mails that may be sent during a certain amount of time, the client will be blocked to relay further mails on the mailserver until the RADIUS server reports that the client has disconnected.