Say you are responsible for setting up an email solution at a company. Which would be your choice? I know of the following options, but many of them not well:

1. Gordano Mail System
2. Exchange
3. Exim
4. Postfix
5. Qmail
6. Zimbra

For having used it a little over two years, I really, really like Gordano Mail System. They offer a whole bunch of things, like calendaring, anti-spam, anti-virus, extremely complete and filterable logging options, aliases, a customizable webmail interface... And their software can be installed on both a Windows or Linux OS. In addition, their support is top-notch, their knowledgebase comprehensive (and, I will admit with a touch of pride, I have contributed, with my questions, to the addition of a few articles in there). Of course, they're not free, which can be a problem, but they're not Exchange, and they do offer pretty much everything that Exchange offers -- which is great if you want to stay away from that, but need all the features. Although, if you need a Blackberry Exchange Server, or something similar, I'm not sure what you should go for.

So.. What would your choice be? Why? I've never played with a more DIY email solution, but I'm sure many people here have and wouldn't trade their setup for the world :)