If you are looking for an email server, check out gmail. What makes Gmail different? It makes sense. It organizes things the way you think they ought to be. It organizes your emails in conversations. You don't have to scroll up and down or resort to find out what you said and when. It is all just in a row, tabbed out.
Just a minute ago, I went to look up a phone number for Fran Leeman. I don't usually keep phone numbers in gmail, but sometimes I do and it is nice when I'm on the road, forgot my PDA and my cell phone is dead, I can look up a phone number in another place. The phone number wasn't there, but every email that I sent and received from Fran was there, listed in order below his name. Wow!!
If you have a blogger account, you can get a gmail account. If you don't, I have 6 to give. I'm telling you, you will be impressed. The only thing it won't do for me is work on my PDA internet explorer. But the way google understands the way people work, it won't be long.