NOTE: You can find an updated version of this article here.
Shared mailboxes are just one of the many great collaboration features of Exchange, and probably the most used one. There is a lot of information about them on the web, for example this TechNet article. Unfortunately, there are still some common misconceptions around them, especially when it comes to ‘missing’ functionality.
Most of those issues are caused by the fact that the shared mailbox is added as additional mailbox or automapped to the primary user mailbox. Outlook however will only expose certain features when the mailbox is added as normal (primary or additional) account. Example of such features/functionality include: Search, Inbox Rules, OOF replies, Categories, To-do lists. Other features will simply not work as expected, for example Private Items, Send on behalf/send As permissions. Another example of why you would need to add a shared mailbox as additional account includes the situation when you would like to perform a Mail Merge and send the messages using the shared mailbox account. This article will guide you on how to add a shared mailbox as a fully functional additional account in the same or new Outlook profile.
First of all, forget about accessing the mailbox directly, it is not possible (anymore). When a shared mailbox is created, a special flag is set on the associated object in AD (ExchangeUserAccountControl), which will prevent you from logging in to that mailbox. In addition, the corresponding user object is automatically created, so credentials are hidden from you. As the administrator you can of course change the credentials, apply a license to the user and try to access OWA/Outlook. Keep trying, it is not possible (anymore) 🙂
So how do you actually access the shared mailbox? The answer is, you need to be granted permissions, much like accessing another user’s mailbox. Full access, with or without Automapping, and recipient permissions in case you need them. The article above explains how you can add those, so I wont bother with the details.
Once the relevant permissions have been assigned, go to Outlook, File, Add Account:
You will be prompted by the familiar Add New Account wizard. Enter anything you want for the name of the Account, and fill in the email address of the shared mailbox. Leave the password fields blank:
Continue to the next screen and wait for the password prompt to appear. This is the important part: once the prompt shows, make sure to enter YOUR user principal name and YOUR password:
In same cases the same prompt might appear a second time, even though you have provided the correct credentials. Just enter your username and password one more time, and provided you have the necessary permissions, the shared mailbox will be added as additional account:
You can then simply press the Finish button to complete the process or configure any additional settings as necessary. If Outlook asks for credentials once you restart the client, make sure to again provide YOUR username and YOUR password.