Issue: User had an E3 license and 50GB of email storage. Added an Exchange online 2 for 100GB of total storage and the 50GB of additional storage was taken up within 7 days

Hello Michael,

As Nick had mentioned, Microsoft 365 E3 license comes with 100GB mailbox quota for primary mailbox and 100GB for in-Place archiving which can be extended when full.

In this case, it is not certain that the affected user was using M365 E3 license prior to the addition of Exchange Online plan 2 license. And there was no need to add the Exchange Online plan 2 license in the first place.

In other way, there is a possibility that local archive was enabled for the user, which still store data within the primary mailbox quota.

Possible Resolution:

• Verify that the affected user was assigned M365 E3 license from the admin center.
• Verify that the M365 license was still active.
• Unassign the Exchange Online license from the user
• Verify that Exchange Online application is enabled for the user.
• Enable In-place (Online) archiving for the user. https://learn.microsoft.com/en-us/purview/enable-archive-mailboxes
• Create and assign retention policy to archive older messages. https://learn.microsoft.com/en-us/purview/set-up-an-archive-and-deletion-policy-for-mailboxes
• Confirm the storage quota of the mailbox Let me know if this was helpful or you need further assistance.