Creating an alias in Outlook (note: you must have Admin permissions):
- In the admin center, go to the Users > Active users page.
- On the Active Users page, select the user > Manage email aliases. (This option will not appear if the person doesn't have a license assigned to them.)
- Select + Add an alias and enter a new alias for the user. (For example, email@example.com) The email alias must end with a domain from the drop-down list.
- Click Save changes.
- Allow 24 hours for the new aliases to populate throughout Office 365. The user will now have a primary address and an alias. For example, all mail sent to John Smith's primary address, firstname.lastname@example.org, and his alias, email@example.com, will go to John's Inbox.
NOTE: If you get an error message "A parameter cannot be found that matches parameter name 'EmailAddresses," it means that it's taking a bit longer to finish setting up your alias, or your custom domain if you recently added one. The setup process can take up to 4 hours to complete. Wait a while so the setup process has time to finish, and then try again. If the problem persists, contact Microsoft Support and they will perform a sync for you.