Python SRS Library is a Python translation of the Perl reference implementation for SRS (Sender Rewriting Scheme) with easy to install packaging and built-in sendmail integration. SRS is needed when forwarding mail for SMTP authorization schemes that publish which IPs are authorized to send mail from a domain (for example SPF - Sender Policy Framework). It can also detect forged SMTP bounces by signing the return path for outgoing mail.
Spammilt is a sendmail-milter which scans email headers for blacklisted relaying servers and locally predefined blacklisted domains/words. By default, when spammilt detects spam, it adds a warning to the header and the subject. It's also possible to reject such emails without bothering the recipient.
The Header and Envelope rewrite mini-HOWTO explains how to rewrite your from address differently in the mail header and the mail envelope. This may be necessary, for example, if your ISP requires you to send mail with one address, but you are subscribed to mailing lists with a different address, or want others to see a forwarding address instead of your ISP's address.
Jsmtpd is a small and modular SMTP server daemon. It is heavily based on plugins, and currently supports spam detection (Spamassassin, Jasen, RBL servers, and BlackList), anti-virus (Clam Antivirus), Recipient rewriting, and many other filters. Filtering is done with a customisable tree of filters. Almost all functionality is implemented as plugins, making it easy to fit your needs.
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.
Sendmail-TLS is a wrapper for Sendmail which allows for clients to make a secure (SSL) connection to their mailserver as described in RFC 2487. The connection is internally forwarded to sendmail and does not require sendmail to be running on port 25. Clients which support this currently are Netscape Messenger, Microsoft Outlook, and Microsoft Outlook Express.