- go to Session Templates
- Add an email address field in the form (manual, joomla or CBfield. the last 2 you can hide for the user)
- Add the field to your message at 'custom messages/pages'
If you always want to have it you maybe can do the following:
- Add the field to the default used session template
- Put same tag to the 'configuration > Attendance messages'
Spamfilters don`t like it when you will use the persons email address in the from header from the email.