How to add users to shared mailbox in outlook

The question on “how to do this with a shared mailbox” is quite common, and the usual answer more often than not remains “add the shared mailbox as additional account in Outlook”. Doing this will expose all the “native” functionalities, including access to Inbox rules, signatures, auto-reply, add-ins, categories, proper search experience, Mail merge, and more. As a general rule of thumb – if you can do something with your regular mailbox, you can do it with a shared mailbox too, as long as it is added the “right” way. This is even needed for “advanced” features that require additional licensing, such as access to the Online archive for a shared mailbox.

Usually, when users are granted access to a shared mailbox, the Automapping functionality is utilized. This is in fact a helpful feature, as it will ensure that the shared mailbox will automagically appear in the user’s Outlook, without them having to perform any additional configuration. As is often the case however, usability comes at a price, in this case the limited set of features being exposed. So while this method might sound convenient at first, you should always check with the user on how they plan to use the shared mailbox and which features they will utilize. Then, use the Add-MailboxPermission cmdlet to grant them Full Access, while toggling the Automapping flag off.

If Automapping isn’t used, the user will have to perform some additional steps in order to access the shared mailbox. Usually, this is done by going to File > Account Settings > Account Settings > double-clicking the user’s account > More settings > Advanced > press the Add button under the “Open these additional mailboxes” section. Another scenario where you would use this method is when you are granting folder-level access instead of Full Access.

I’ve also seen quite few people go the “unsupported” route of logging in to a shared mailbox directly. Yes, this is technically possible in Exchange Online, always has been. However, it is not something that Microsoft supports and while it’s hard to find a document that clearly spells this scenario as going against the license agreement, rest assured that this is not something the licensing folks will approve of.

So after this lengthy introduction, let’s finally go over the steps to add a shared mailbox as additional account in Outlook. Unless otherwise noted, the instructions below apply to the most recent click-to-run version, which at the time of writing is Version 2110 (Build 14527.20276 on the Current channel).

To start with, hit the File menu, then under the Info pane, hit the Add account button:

Now, this is the most important part of the process. As you can note from the screenshot below, the credentials we are being asked to provide are for the shared mailbox account. This is not what we should do. Instead, press the Sign in with another account link, as highlighted below:

This will take you a step back to the initial login screen, where you need to enter the username. Make sure to enter your *own* UserPrincipalName here, in the format . Some variations might apply depending on how authentication is handled in your organization, but the thing to keep in mind is that you should be providing your own credentials!

Once you enter the username, press the Next button and complete the authentication request. Again, depending on the tenant setup, and the authentication methods configured for the given account, the steps will differ here. In my case, a passwordless authentication prompt was triggered, as shown below:

If everything goes OK authentication-wise, the process is now complete and Outlook will present you with the following dialog. As stated therein, you need to restart Outlook for the changes to take effect, so go ahead and do so at this time.

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