For anyone interested in a commercial MTA, check out SurgeMail - it is commercial, has a lot of nice features, web interface, built in webmail, and with the 3.1 version, they are bundling in their previously optional filesharing/calendar app - SurgePlus. And for pretty decent prices I think - http://www.surgemail.com/surgemail/pricing.htm

For example:
      5 user license - $Free
  100 user license - $470
1000 user license - $570 and so forth.

I am moving most of my domains from CGPro to SurgeMail. Dale