Email server for windows

Look for a good email server for windows other than exchange server

do you guys have any recommendations?

only need IMAP/POP3/SMTP and SSL support

for small biz use, no more than 100 users 20 domains

I've tinkered with hMailServer.

http://www.hmailserver.com/

Here's another vote for hMailserver. I've been using it for about 9 months for those domains we don't want to include on our Exchange server (don't ask, that's just the way it is). I also use it for my personal domain and my family can access their email from anywhere via the webmail interface provided by the Squirrelmail. That's real handy when you're travelling.

I saw a alt-n MDaemon installation with around 200 users a few years ago, and that company was happy with it. It is a product that has been around for years now.

For the small-biz space I'm quite happy with Kerio -- but I have never worked professionally with their Kerio Mailserver product, so I have no direct experience with it. It gets very good reviews from time to time...

My solution of late has been Google Apps. I'm super-happy with it:

• Uptime is as good as any self-hosted solution in the smallbiz space will see
• The feature set works O.K. for smaller companies
• Having one system less to administer and maintain is a real relief.

Perhaps not ideal for your 20 domains requirement though -- you can add domain aliases to a Google Apps account, but I don't know how many it will take, and usernames will be shared across domains. One potential workaround is to make multiple accounts of course..