According to this article re: business applications:
http://smallbusinessbonfire.com/can-...ess-profitable
Specifically, It mentions that email site should have their domain name as a sign of professionalism but also that can be easily attained through apps such as a FREE one mentioned about Mozilla, or I believe a google app for a minimal price was mentioned earlier. This is not only about presentation but about not having all your email web-based and having some solid back up.
PS: This is really a good article...also names the few basic types of software every business should have etc.