Anti-Virus

Clam AntiVirus (ClamAV), is a widely used free antivirus software toolkit for Unix-like operating systems. It is mainly used with a mail exchange server as a server-side email virus scanner. ClamAV is open source software distributed under the terms of the GNU General Public License (GPL). Both ClamAV and its updates are made available free of charge.

Ref :http://en.wikipedia.org/wiki/Clamav

For more information on ClamAV please visit their website:
http://www.clamav.org

Anti-Spam

For Spam we employ three systems.

DNSBL

DNSBL is an abbreviation that stands for "DNS blacklist". It is a means by which an Internet site may publish a list of IP addresses that some people may want to avoid and in a format which can be easily queried by computer programs on the Internet. The technology is built on top of the Internet DNS or Domain Name System. DNSBLs are chiefly used to publish lists of addresses linked to spamming.

Ref :http://en.wikipedia.org/wiki/DNSBL

Greylisting

Greylisting (sometimes spelled graylisting) is a method of defending electronic mail users against e-mail spam. A mail transfer agent which uses greylisting will "temporarily reject" any email from a sender it does not recognize. If the mail is legitimate, the originating server will try again to send it later, at which time the destination will accept it. If the mail is from a spammer, it will probably not be retried, and spam sources which re-transmit later are more likely to be listed in DNSBLs and distributed signature systems such as Vipul's Razor.

Ref :http://en.wikipedia.org/wiki/Greylisting

SpamAssassin

SpamAssassin is a computer program released freely under the Apache License 2.0 used for e-mail spam filtering based on content-matching rules, which also supports DNS-based, checksum-based and statistical filtering, supported by external programs and online databases. SpamAssassin is generally regarded as one of the most effective spam filters, especially when used in combination with spam databases.

While simple text-matching alone may, for most users, be sufficient to correctly classify a majority of incoming mail the complexity involved in the combination of the comparison of words and symbols used in conjunction with the sources of spam may far exceed the average user's capability. For instance, graphic-only spam messages have no text to compare to therefore checking the sender's originating mailserver and included links against various databases of known e-mail abusers enables the prevention of unnecessary or non-personal mail getting through to the end user.

Ref :http://en.wikipedia.org/wiki/SpamAssassin