A shared mailbox is a type of user mailbox that doesn’t have its own user name and password. As a result, users can’t log into it them directly. To access a shared mailbox, users must first be granted Send As or Full Access permissions to the mailbox. Once that’s done, users sign into their own mailboxes and then access the shared mailbox by adding it to their Outlook profile. In Exchange 2003 and earlier, shared mailboxes were just a regular mailbox to which an administrator could grant delegate access. Beginning in Exchange 2007, shared mailboxes became their own recipient type:

• RecipientType: UserMailbox
  
  
• RecipientTypeDetails: SharedMailbox
  
  

In previous version of Exchange, creating a shared mailbox was a multi-step process in which you had to use the Exchange Management Shell to complete some of the tasks. In Exchange 2013, you can use the Exchange admin center (EAC) to create a shared mailbox in one step. For details, see Create a Shared Mailbox. In fact, the EAC has a feature area devoted entirely to shared mailboxes. Just navigate to Recipients > Shared mailboxes to view all the management tasks for shared mailboxes.

You can configure the shared mailbox with the following delegate permissions:

• Full Access   The Full Access permission allows a user to log into the shared mailbox and act as the owner of that mailbox. While logged in, the user can create calendar items; read, view, delete, and modify email messages; create tasks and calendar contacts. However, a delegate with Full Access permission can’t send email from the shared mailbox unless they also have Send As or Send on Behalf permission.
  
  
• Send As   The Send As permission allows a user to impersonate the shared mailbox when sending mail. For example, if Kweku logs into the shared mailbox Marketing Department and sends an email, it will appear as though the Marketing Department has sent the email.
  
  
• Send on Behalf   The Send on Behalf permission allows a user to send email on behalf of the shared mailbox. For example, if John logs into the shared mailbox Reception Building 32 and sends an email, it will appear to recipients as being sent by “John on behalf of Reception Building 32”. To grant Send on Behalf permissions, you must use the Exchange Management Shell. Use the Set-Mailbox cmdlet with the GrantSendonBehalf parameter.
  
  

In previous versions of Exchange, you could use a regular mailbox as a delegated mailbox. If you have delegated mailboxes, you can use the Shell to convert those delegate mailboxes to shared mailboxes. For details, see Convert a User Mailbox into a Shared Mailbox.