We run Exchange 2013 here in-house, but do not use Exchange for MTA. In my perimeter network, I have hMailServer. This free, open source system runs on Windows, has AD integration, and extensive AV and AntiSPAM capabilities. In fact, it's our email content-filter gateway for Exchange back-end. We also host several small business clients directly on this server with POP and IMAP access.
Easy to install and manage. It also interfaces nicely with SquirrelMail for a web-based interface. I also publish the admin console so my clients can add/change/remove user accounts directly. It's designed for ISP use and has been tested with tens of thousands of user accounts across multiple domains.
Highly recommended!
Glenn
_________________________
Actually I
am a Rocket Scientist!
