A user can have any number of email addresses, but only one default email address. The default email address is the address that outgoing email will appear to have come from and where replies will be sent.
To change the default email address for a user:
- Log on to the server running exchange server. (This is necessary because Active Directory Users and Computers does not display the necessary “E-Mail Addresses” tab if you try this from a different server.)
- Run Active Directory Users and Computers.
- Navigate down to the user account.
- Open the properties for the user account.
- Open the “E-Mail Addresses” tab.
- Highlight the SMTP address that is to be the new default email address.
- Click [Set As Primary]