Allow admins the option to make the email mandatory or optional for additional/accompanying guests.

Currently it is not mandatory for accompanying guests to input an email address. Admins should have the option to make it mandatory or optional.

Eg: If you've got guests coming to a conference and you want to communicate content received/follow-up with participants post-event.

It should be optional as its not always appropriate for every transaction. Definitely not applicable for every event, but if you are doing a conference or seminar type event with material/deliverables it would be really good.