Restore Mailbox in another/new mailbox
the reason is, if the mailbox gets restored, all mails get lost, which are newer than the restore point.
If the restore process could be restoring in e.g. <firstname.lastname@example.org> (a new mail account), than the user can pickup his lost mail(s) from the other account without loosing mails he got after the restore point.
After that, the user can delete this restored mailbox account. Perhaps set the account to not receiving mails.This is more relevant, if you are using mdbox accounts.