Opening another mailbox in Outlook on the web
After logging into Outlook on the web (https://outlook.office.com/mail/), click on your picture/icon in the top right to get to the menu shown below.
Click Open another mailbox in the menu
This box should pop up, type in the email address of the account you are wanting to access.
I’m using postmaster@berea.edu in this example.
Click on the account to select it.
Click Open to open the mailbox in a new tab.