Businesscomputingworld posted a review on the Ipswitch IMail Server Premium

Everything a small business needs in a messaging and collaboration server is available in the Ipswitch IMail package and it's certainly a lot easier to setup and manage than Exchange. It's cheaper too, and definitely worth considering. However, it's not the only alternative with a number of competitors that are just as easy to live with, if not easier, especially from the user perspective. Lastly, it's worth just mentioning that the e-mail server market is going through a period of rapid change at present, as the ready availability of fast broadband links makes hosted e-mail services a lot more viable. Google has really upset the apple cart here, with its Google Apps Premier business offering while other providers offer hosted Exchange where you simply rent the mailboxes you need, leaving someone else to worry about the server hosting them.

Ipswitch IMail Server Premium v11.01 Review