It probably was using a bayesian filter of some sort. There are many, I use bogofilter because my email app comes with it, and there is HNer jgc's popfile.
Actually setting up a multi-user SMTP and IMAP server on Linux is straightforward if you've done it before, or it is here-be-dragons stuff if you haven't. (Your distro might configure it all up for you prepackaged, or you could be in for a lot of reading.) Integrating the bayesian filter is probably the easy part.
If it is only for you, it is perhaps easier to integrate it with your email app rather than at the server level. Popfile will do that.
Actually setting up a multi-user SMTP and IMAP server on Linux is straightforward if you've done it before, or it is here-be-dragons stuff if you haven't. (Your distro might configure it all up for you prepackaged, or you could be in for a lot of reading.) Integrating the bayesian filter is probably the easy part.
If it is only for you, it is perhaps easier to integrate it with your email app rather than at the server level. Popfile will do that.