Personal proxy
You can run a small proxy application on your client computer that will connect to your mail server, get the email, run SpamAssassin on it, then deliver to your email client.
That's a personal proxy server.
[http://sourceforge.net/projects/imapassassin ImapAssassin] is a perl application which uses SpamAssassin to pre-filter an IMAP mailbox for spam, before you download it.
[http://www.nospamtoday.com/workstation No Spam Today!] POP3 Proxy for Workstations (Windows 98SE/ME/2000/NT/XP/2003) easily connects to any POP3 email client, and provides a wizard to enable spam protection for all your Outlook POP3 mail accounts. It's $30.
- Pop3Proxy and SaProxy : Windows (free open source) proxy based on Dan Mc Donald original work. Setting up Pop3Proxy, and some versions of SaProxy, is *not* point-and-click easy, however. Altought there was one SaProxy version point-and-click easy, it is outdated (it includes an old version of SA)
- SaProxy Pro : by Bloomba, derived from SaProxy; Windows proxy that's easy to set up and works quite well. It's $30. Seem to be some claims regarding support
Site-wide proxy
You can also set up a spam proxy server that receive all your organization's incoming mail, filters it, and pass it to your organization's legacy mail server.
No Spam Today! SMTP Proxy - [http://www.nospamtoday.com/server] - The easy-to-use setup of No Spam Today! requires just a few mouse-clicks to set up a complete SpamAssassin runtime installation on a Windows server (supports Windows NT/2000/XP/2003). Our SMTP proxy software makes it easy to integrate No Spam Today! for Servers into any existing SMTP infrastructure.
- any MTA configured as a satellite system and running SpamAssassin will do that (see IntegratedInMta). However, setting up an MTA requires careful configuration.
The [http://www.amavis.org/ Amavis] mail scanner can be set as a SMTP to SMTP proxy. Amavis sits between two SMTP mail relays, receives incoming mail, filters it through SpamAssassin or an optional virus filter, and drops, bounces or marks spam messages. Though you can't use personnal settings, it's very flexible and does not require you to mess with your MTA's configuration.
[http://www.mailscanner.biz/introduction.html MailScanner] can be used in a similar way to Amavis.
[http://www.worlddesign.com/index.cfm/rd/mta/spampd.htm] SpamPD can be used as an SMTP or LMTP proxy server. Other than amavis, it uses the original SpamAssassin style header/subject tags. It can't do anti-virus scans though.