>Obviously postfix in itself would do fine, but what about a web >interface and all of the end user provisioning capabilities.
well, obviously the whole world doesn't run Win32 mail servers. there's a wide choice of webmail, pop, imap opensource servers. integration is the key. You really shouldn't try it if you don't have a fairly solid *nix sysadmin. there are a lot of decisions to be made, esp if you want to scale to large volumes of mail and mailboxes, plus integrating with other systems like billing. But it is do-able. I set up a FreeBSD postfix + qpopper + bind9 + apache + ftp all-in-one box for a Men & Mice customer. Works fine. but the box is self-contained and low volume. Len >Exim? >Imp?
