Understanding Shared Mailboxes in Office 365 (updated)

Many potential customers are asking about departmental mailboxes in Office 365. How can a department, a team etc share a mailbox, and does it involve a license?

Shared mailboxes in Office 365 Exchange Online allow a group of users to view and send e-mail from a common mailbox.

A shared mailbox:

  • doesn’t have a username and password, so users cannot log on to it directly. A user must sign in to his/her own mailbox and then open the shared mailbox using Send As permissions
  • don’t require a license, but each user that accesses a shared mailbox must be assigned to a subscription plan
  • cannot be accessed by users with Exchange Online Kiosk subscriptions
  • has a maximum size of 5 GB. Exceeding this limit will require an Exchange Online plan 1 subscription (see Note 1 below )
  • can be used to store emails sent to and received by the shared mailbox
  • can be used to store data migrated from on-premises public folders
  • cannot be used to archive e-mails for individual users

In Office 365 Exchange Online, shared mailboxes are created only via Remote PowerShell. See the article "A couple of tips for setting up Shared Mailboxes" - link for more details. Update March 26th 2012 - new GUI based tool for creating Shared Mailboxes

Note 1 -- From an Exchange perspective a shared mailbox is just a 5GB mailbox provisioned to a disabled user account (and delegated to a bunch of SG/Users). So when reaching the quota, mailbox will start receiving warning messages (10% prior to the quota) and then will start blocking mail sent from it (if “send as” as been granted and ‘from”  used) and finally it will refuse accepted new e-mail (with “mailbox is full” in the NDR).


See also