Send and receive email from any server. You do not have to change a thing. Use your existing email. You don't even have to change your work flow. Any email sent from OZ will be in your out box of whatever email you presently use. All email conversations will be stored in your event for a historical record of all communications.
Oz's email feature alone would be reason enough to sign on. Look at all the rich features available to you when composing an email.