Enable registration tracking mode to pre-register people for events. After the event, you can mark which ones attended or did not show up. You can use the attendance listing to generate mail merge letters to those with certain attendance settings (e.g., send letters to all who registered but did not show up in order to invite them to attend the next event).
Activate Registration Tracking
In order to start tracking registration you need to activate it for an event. To do so, click on the Track Registrations button in the row of function buttons at the top of an event record.
You may also edit the event and check the Track Registrations checkbox in the settings box on the right side of the form.
Now when you list the attendees of the event, they will be called registrants. There will also be an attendance widget next to their name with clickable icons which allows you to set whether to mark the person's registration status as one of the following: Registered, Attended, Walk In, Canceled, and No Show.
Also in above the list of registrants, you'll see this menu bar which allows you to delimit the list to just the people who are marked as Registered or Attended, etc.