Thanks to all who offered help and comments. I now have exim as my MTA, and I'm very pleased with the results. The filtering facilities are nice - replaced what I previously used procmail for. I don't think there's anything I needed to do but couldn't with smail/procmail, which I can now do with exim (my needs are pretty limited) but the documentation available for exim is superb, which makes a heck of a difference...
Thanks again, Paul.
