Accept replies by e-mail from multiple addresses

Quite often, users have multiple e-mail addresses. The original ticket gets submitted from a computer using the main e-mail but then for the follow up, users reply via mobile phone where they are using a different e-mail address.

The same applies to companies, where different staff members in a department handle the same jobs.

All replies that do not originate from the main e-mail address get rejected by RSTickets!Pro.

It would be useful if staff members and users could add multiple e-mail addresses to their account, letting RSTicket!Pro know that it's OK to accept replies from these e-mail addresses.

For security and privacy reasons, users should only be able to add a second or third e-mail address if the address has been confirmed with some kind of security check (e.g. send confirmation e-mail, where user has to click on a link). For staff members, it should be possible to just add a second or third e-mail in the backend without confirmation.