Good morning Kevin-
By going to linux, as pointed out, your email server can be used to do some simple virus scans by using a service such as procmail. Procmail is a package that uses a ruleset to determine what and or how a particular message is to be handled. It can be used to filter unwanted spam (to some degree), filter out viruses, forward messages to additional places.
As for SMTP servers, there are two that seem to be popular.
The "traditional" server is sendmail. This has been on 'nix systems for many years and comes with most distributions.
The second is exim, which I haven't used, but is said to be much easier to configure.
will get you there.
Being a "traditional" (read as old fart) unix guy, I use sendmail for my mail server. I did not find it too difficult to set up and it is a breeze to maintain.
As to distributions, I have used both Debian and Redhat.
It is my feelings that Red Hat provides a much more friendly configuration environment for a newbie to linux than what is provided by Debian. A "typical" Red Hat distribution does take more disk space than a debian "typical" debian installation. However, for ease of use and getting started, I feel that the Red Hat might be more "user friendly". If you have a disk drive with about 2 Gig of space, you will be fine. The Red Hat "defaults" to loading more packages than Debian. You can certianly use both to load or not load as many packages as you want ;-)
Both are fine distributions. Both are available over the
internet for free. You should however, have a high speed link as you will be downloading a couple of CDroms of data for your efforts. Both are also available at nominal cost as CDroms, either by mail order or in larger computer stores.
By all means also look to your local community for linux users groups. In our area (Silicon Valley) our local group has "install parties" monthly. You bring your box and distritbution, and someone that has already blazed the path will help you install it! Also local colleges in your area might provide assistance with the installation.