Net_NNTP is a PHP/PEAR library for communication with NNTP servers. Net_NNTP handles connection and protocol-level commands (RFC977), including many non-standard commands (RFC2980), via a user-friendly API which hides the actual NNTP commands/syntax. Some knowledge about NNTP and general knowledge about email and MIME is required, since parsing of content and headers is left up to the user. Net_NNTP allows advanced users direct usage of NNTP commands via the separate protocol implementation. Net_NNTP includes a fully-functional NNTP to HTML gateway demo application.
purepost is an interface between Courier-MTA and Sophie for virus scanning. You can have it check mail for all your users, or just a few. Using courier's dot-courier functionality, this script intercepts an email before it hits the mailbox, creates a temporary file, tells sophie to scan that temporary file for viruses, and if it finds a virus, denies delivery and notifies the sender (otherwise it allows the message to be delivered).
JSpamfilter is software that intercepts connections from remote Internet mail servers before they can connect to your mail server. The originating IP address for the inbound connection is then checked against one of the DNS-based SPAM Blackhole (DNSBL) lists maintained on the Internet by various organizations. If the check passes, the connection is allowed to proceed to your mail server; if it fails, the connection is told that the mail server is unavailable, then dropped.
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.