Shared mailboxes and Microsoft 365 licensing

Standard shared mailbox rule

• A shared mailbox can store up to 50 GB of data without assigning a licence to the shared mailbox itself.
• Users accessing the shared mailbox must have their own licensed Exchange Online mailbox.
• Shared mailboxes are intended for delegate access, not direct sign-in; Microsoft says sign-in for the shared mailbox account should remain blocked.

When a shared mailbox needs licensing

• More than 50 GB primary mailbox storage requires Exchange Online Plan 2.
• In-place archiving requires Exchange Online Plan 2 or Exchange Online Plan 1 with Exchange Online Archiving.
• Litigation hold requires Exchange Online Plan 2 or Exchange Online Plan 1 with Exchange Online Archiving.
• Advanced features such as Microsoft Defender for Office 365, Microsoft Purview eDiscovery (Premium) or retention policies may require additional licences.

Common decision points

• Use a shared mailbox for team email addresses where multiple licensed users need access.
• Use a Microsoft 365 group if too many users need access or if you need a different collaboration/security model.
• Review archive, retention and compliance requirements before assuming a shared mailbox is licence-free.