A common request we receive is to correct the email addresses of mail-enabled contacts. For instance, if your agency has a contact for
firstname.lastname@example.org, it will display in your global address list and offline address book as
This is entirely normal behavior. Microsoft Exchange Server requires there to be two different email addresses for any mail-enabled contact. The first address is the ExternalEmailAddress. This is the address to which the system will send messages. In our example, this is
The second address, and one that is required for every mail-enabled object in the system, is the PrimarySmtpAddress. This is the address from which the system will receive messages. Because the system does not have
contoso.com as an accepted domain, this address must be, in our example, at
Please note that Exchange Online does not allow mail-enabled contacts to receive messages from external sources; only internal mailboxes and distribution groups may address these objects.
To fully understand how this functions, here is a list of steps that are taken to deliver an e-mail to your client.