In Outlook, it is possible to add multiple sending addresses. To do this, follow the below guide.

Firstly, open an Email in Outlook as a new window. Then, in the top toolbar, navigate to the 'Options' section and there is a 'From' section:

Selecting the 'From' option will display a new field in the Email that is currently being composed, as shown below:

As highlighted here, also, there is an option for 'Other Email Address'. Select this.

A box titled 'Send From Other Email Address' will then appear. Here, enter the alternate address Emails are going to be sent from:

This address will then be in the 'From' list:

Should the necessary permissions be applied to allow for sending from that address, you will now be able to send Emails from the address.