Self-Help Desk Feature: Email Log to/from Users
Help desk employees can choose to send personal or "tracked" emails to Problem Report/Service Request users. If tracked, the email thread is saved to the database, and is visible on the Tracked Email tab:

With the email logged, all help desk employees can follow up on user requests.
The email thread can also be seen in the Requests by\Requestor Email view:

Notice how the email is associated with the Problem Report/Service Request (a twistie appears if there are emails associated with a Problem Report/Service Request). Outgoing emails are given the white envelope so you can easily identify them.
To accommodate the user who does not use Notes mail, the MailProcessor agent is responsible for making incoming Internet messages responses to the appropriate Problem Report/Service request document.