Why can't I use duplicate email addresses

Thank you for your reply but that is the wrong email address field, the one I am referring to is User Details, General Settings. The one blocked in red below. I have been told the problem has something to do with RingCentral's single sign on product. I do get why they might care if we used single sign on, but the failure in their logic is that every email address attached to a phone number will be logging in. We reuse an email for all of the conference rooms so that the emails go to one mailbox. I don't know what emails go to the main email address that I am concerned about. I'm guessing voice mails, missed calls, password changes. But those can all go into a dump mailbox because who cares that a missed call to an empty conference room was missed. The Notifications that you mentioned can be anything, no problem with duplicates there.

@jenn-community-moderator