Outlook - change email sender

If you have permissions on multiple mailboxes, you can change which account you send from.

Start a new email

Click options at the top, then click the From box.  This will make a From dropdown appear.

Use the dropdown to select which address you want to use to send the email.

This should always default back to your primary email address on your next email so remember to do this for each email you need to send from another account.