In Exchange 2013 there are regular Mailboxes and there are Shared Mailboxes. The latter are user independent Mailboxes and have common email addresses, for example info@contoso.com or sales@contoso.com. These Mailboxes don’t have a specific user account but are mostly shared between a number of users.

The interesting part is that you don’t need a license to implement a Shared Mailbox (or a Resource Mailbox for that matter) but the users that access the Shared Mailbox need to be licensed though.

There used to be a 10 GB size limit on Shared and Resource Mailboxes, but this was changed recently (November 2014) and all Shared and Resource mailboxes are now restricted to 50GB, just as regular Mailboxes. You can check this on the Exchange Online Limits page on Technet.

To create a Shared Mailbox (in Office 365 Small Business) login to the Microsoft Online Portal, click on Users & Groups and in the Users & Groups window select the Shared Mailboxes tab.

To create a new Shared Mailbox click the + Icon, enter a Mailbox name and an Email Address:

When using a Shared Mailbox there needs to be (at least) one user that needs Full Access to the Shared Mailbox, and you can add this user in the add members window. Use the + Icon to select a user in the people picker window.

Click Finish and the Shared Mailbox will be created and the user will be granted Full Access. When you navigate to the Exchange Admin Center (https://outlook.office365.com/ecp) and select Shared in the Recipients section you’ll see the new Shared Mailbox.

When you open this Shared Mailbox and select Delegation you’ll see that the user has Full Access and Send As permissions:

Of course it is also possible to create Shared Mailboxes in Office 365 using Remote PowerShell:

$Cred = Get-Credential admin@contoso.onmicrosoft.com
$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://ps.outlook.com/powershell/ -Credential $Cred -Authentication Basic -AllowRedirection
Import-PSSession $Session

New-Mailbox -UserPrincipalName sharedmbx@contoso.com -Name "Shared Mailbox" –Shared

The –Shared option will create a Shared Mailbox, but you can also use the –Room option to create a Room Mailbox or the –Equipment option to create an Equipment Mailbox. All three however are Resource Mailboxes.

Granting permissions to access the Shared Mailbox is not difficult with Remote PowerShell. To grant Joe’s Mailbox Full Access to the new “Shared Mailbox” you can use the following command:

Add-MailboxPermission –Identity sharedmbx@contoso.com –User joe@contoso.com –AccessRights FullAccess

Or similarly

Add-MailboxPermission –Identity sharedmbx@contoso.com –User joe@contoso.com –ExtendedRights "Send As"
Set-Mailbox –Identity sharedmbx@contoso.com –GrantSendOnBehalfTo joe@contoso.com

Convert an existing Mailbox

When you have an existing Mailbox and want to convert this to a Shared Mailbox you have to use PowerShell since the Exchange Admin Console doesn’t have this feature.

To connect to Exchange Online using PowerShell you can use these commands:

$Cred = Get-Credential jaap@contoso.onmicrosoft.com
$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://ps.outlook.com/powershell/ -Credential $Cred -Authentication Basic -AllowRedirection
Import-PSSession $Session

The Get-Mailbox command will retrieve a Mailbox, and you can request the RecipientTypeDetails to check the type of Mailbox. This command is:

Get-Mailbox -Identity info@contoso.com | Format-List RecipientTypeDetails

To convert this mailbox to a Shared Mailbox you can use the Set-Mailbox command:

Set-Mailbox -Identity info@contoso.com -Type Shared

In the Microsoft Online Portal you can remove the existing license from the Mailbox (if there was one assigned to the Mailbox) since it is no longer used. Don’t let the warning message fool you.

This is what the warning message says:

Are you sure you want to remove the Exchange license?

• The user’s mailbox and all messages in it are deleted. We recommend that you only delete licenses from users who no longer need email.
• All email aliases associated with the user account are deleted. If you need someone in your company to receive email at those aliases, assign them to another user.
• Their Lync Contacts list may be deleted. To restore their Lync Contacts, assign the user an Exchange license within 30 days. If you want to remove their Exchange license but keep their Lync Contacts, contact Support before you remove the Exchange license.

While this is all true for a regular Mailbox it does not apply to a Shared or Resource Mailbox so it’s safe to continue.