At Hex, we always use Google Apps for our clients when we set up a hosting service for them. They'll be able to send emails using their own domain while taking advantage of Google's email infrastructure. Excellent features like anti-spam and Gmail's UI for accessing email has been invaluable.
All these that comes for free has sadly come to an end. The only good news is that if you've previously signed up for free, you can keep using it for free.