We want to use UDFs in mass emails that are based on drag-and-drop templates. (This is not currently available for emails using a drag-and-drop template.)

Today's specific need: send a mass email to those who have RSVP'd for various events in our upcoming conference, and include in the email the list of events they are registered for. We tagged their chosen events in a multi-select UDF when they completed the DIY registration form.