How to open another mailbox in Office 365 To Parent Forum June 30, 2021 at 10:14 AM #1301 Chris MathewsKeymaster Did you know that you can open a delegated or shared mailbox in Office365 using a browser? It is fairly simple and should take you no time at all. First, open a browser (Chrome, Firefox, Edge, or even Internet Explorer) Go to https://outlook.office.com Sign in with your username and password Left-click on the icon (might be your initials or a picture of you set one) Select “Open another mailbox” Enter the mailbox you wish to open If you are delegated to the mailbox it will open, if not, you will get an error. If you get an error, contact your IT department for more information. If you were just added to the mailbox as a delegate, it can take up to sixty (60) minutes for the permissions to take effect You must be logged in to reply to this topic.