Why manage email names?
The point of focusing on just the left-hand side instead of the whole email address is to prevent the problem of John A. Doe getting john.doe@emory.edu and John B. Doe getting john.doe@emoryhealthcare.org Both would be in the same directory. Having two different people with the same email name is confusing, and can lead to a person getting email intended for someone else. Requiring an email name to be used by only one person helps to prevent such confusion and allows Jane Doe employed by Emory Healthcare with address jane.doe@emoryhealthcare.org to have the address jane.doe@emory.edu if she becomes employed by the University, and vice versa. It also allows a doctor named Jim Doe to have both jim.doe@emory.edu and jim.doe@emoryhealthcare.org (those would go to the same Enterprise Exchange mailbox).
