Apache SpamAssassin is an extensible email filter that is used to identify spam. Once identified, the mail can then be optionally tagged as spam for later filtering. It provides a command line tool to perform filtering, a client-server system to filter large volumes of mail, and Mail::SpamAssassin, a set of Perl modules allowing Apache SpamAssassin to be used in a wide variety of email systems.
mkrdns is a small Perl script that helps automate changes to your DNS zone files. It does this by reading your named.boot/named.conf file to find all the domains/networks for which you are authoritative. It then reads all of the forward zone files and generates PTR records which it inserts in the reverse zone maps.