I am trying to fully understand the downfall of allowing duplicate emails in a contact list. Here is some context: We will have multiple contacts from the same family unit. Using a different email address for each person in the family is difficult and cumbersome for the user. If we allow duplicate emails, we can still segment and personalize messages and invitations to surveys. So that would be fine.

But, if a user does make another contact with us, forgetting that they are already in our system, we will have duplicate contacts. And these duplicate contacts would have to deleted manually? Because we can set rules to merge contacts, but these rules cannot be stacked. For example, we cannot merge contacts with the same email AND the same first and last name. The system will only search for one at a time. 

Is all of this correct? Am I leaving anything else out about the cons of allowing duplicate emails in our XM directory?

Thanks :)