SpamAssassin is one of the best spam filters and it is also free. However, it usually runs on corporate UNIX servers. The goal of this open source project is to release special builds of SpamAssassin that run on Windows platform.

The result is very high precision of email classification: the filter properly identifies and marks nearly all spam messages, while the false positive rate, that is, the amount of incorrectly classified legitimate mail, is virtually zero.

SAwin32 supports SSL and works with any email client (Outlook, Eudora, etc.), but only with POP3 mail accounts. Thus, it will not work with web-based email (such as Hotmail), IMAP, Microsoft Exchange, Lotus Notes, etc. In order to use this filter, you need to know the name of your POP3 (incoming) mail server. It typically looks like pop.isp.tld. You can find it in the configuration of your email client or by asking your Internet Service Provider.

The history of the filter started in 2002, when Dan McDonald successfully ported SpamAssassin to Microsoft Windows by writing pop3proxy Perl script that was acting as a proxy between the mail client and the POP3 server.

Further work on this script lead to the release of the free spam filter SAproxy and then commercial SAproxy Pro.

Soon after the release in 2003, Consumer Reports declared SAproxy the best personal anti-spam solution for Windows. However, after Yahoo! acquired Stata Labs at the end of 2004, they announced that SAproxy was discontinued. In 2005 Eugene Pivovarov adapted free SAproxy v1.2 so that it started to work with the latest versions of SpamAssassin, DCC and Vipul's Razor. After the project moved to SourceForge, it got the name SAwin32.