Originally Posted by
ScottC
Take a look at Google for domains. I find their spam filtering to be the best out there, it'll easily do 25 people and everyone can still use their own email client (or the web frontend). It's easy to set things up and you can keep web and other services hosted elsewhere and only use Google for the email portion.
http://www.google.com/a/help/intl/en/index.html
+1
I've migrated my domains over to Google hosted apps and have been incredibly happy with the spam solution, among other things. You can enable IMAP and/or POP3 or just use the web interface. It supports things like a custom URL for the web access (webmail.companyname.com), creation of groups, shared calendaring and some other neat features. It isn't great for shared mailbox access like Exchange/Outlook is, but should definitely meet the needs of the company as you've described them.