Well, if it's a client you need, it won't be running on e-smith, but on your users' workstations. Have you tried Eudora? It has a subscription version (i.e. with a small advertising box in lieu of payment). It is a bit of a resource hog, but has good features, including a good rules engine. On the other hand, there's always Outlook Express, which is included with IE 5.x.
Des Dougan