Due to the needs of work and needing the ability to reproduce stuff at home when I'm telecommuting, I run a copy of Exchange here. I hate it. It's just me and my wife so there's no need for such a beast of a system for our mail.
So, I want to dump Exchange and drop using Outlook and move to Thunderbird as a mail client. But what mail server can I use? The nice thing about Exchange is that it's tied into my directory which makes adding aliases easy. See, when I sign up for something, I automatically add an alias to my mail account through LDAP so, if that address starts getting spam I can kill it with ease. I want the ability to still have 145 different aliases to my main address.
A little spam blocking is nice, plus the ability to control security on inbound connections and relays is imperative. The last, and very important part is that it must run on Windows Server 2003.
Any ideas of good mail servers that are somewhat inexpensive?