We want to be able to identify an email address (or maybe a phone?) as being shared across records, and who it's shared with. If the email becomes invalid, we want to be able to mark it once and update all instances of that email, as we can currently do with addresses. We are currently duplicating the addresses and using comments when we can, but SharonAndJim@email is technically a personal, valid email for both Sharon and Jim, until it isn't. We also have admin assistants' contact details on their boss's record, or parent info on children's records, etc.