Adding E-mail Aliases in Office365

There are some instances where you wish to map alias email addresses to an account in Office365 (Office Online). To do so follow these steps:

Login as an Administrator.
In the sidebar under Management, click Users.
On the Users page, click on the Display Name of the user for whom you'd like to add an alias.
At the top of the User Settings page, click on More.
Under Additional service-specific settings -> Microsoft Exchange, click on Change Mailbox Settings.
A new window will open. Expand the Email Options pane.
Click Add.
Type in the alias and choose the appropriate domain name.
Click OK.