Configuring User Email Addresses
(Exchange 2019, 2016 & 2013)
To configure user email addresses in Exchange 2013, 2016 or 2019, log into the Exchange Admin Center and select Recipients on the left navigation bar. Select Mailboxes at the top and double-click the mailbox to modify the email addresses.
In the mailbox details, select email address on the left. The list on the right shows all of the email addresses assigned to the user. The SMTP addresses in this list represent all of the addresses which the user will be able to send as using Exchange Custom Sender. Use the plus button to add a new SMTP address.
The default address is the one highlighted in bold, which also has the letters SMTP in capitals.