Has anyone else seen newly provisioned Exchange Online mailboxes inherit incorrect MaxSendSize and MaxReceiveSize values? Between July 30 and August 12, 2026, 79 of 169 new mailboxes in our tenant were affected. Mailboxes created from July 30 through August 7 received 35 MB and 36 MB limits, while those created from August 10 through August 12 received only 150 KB for both limits. Mailboxes created after August 17 appear to be provisioning correctly at 150 MB.
Our environment uses Exchange Online with users synchronized from on-premises Active Directory through Entra Cloud Sync. There is no on-premises Exchange server or hybrid configuration, and the relevant on-premises Exchange attributes are not present. Users receive licenses through dynamic groups, and all four mailbox plans are configured for 150 MB. The problem affected regular users, shared mailboxes, and service accounts regardless of license type.
I verified the mailbox plans, organization and transport limits, and audit logs. There were no customer-side Set-Mailbox, New-Mailbox, or Set-MailboxPlan operations changing these values, and manually correcting an affected mailbox with Set-Mailbox remains effective. Interestingly, all mailbox plans showed a nearly identical WhenChanged timestamp around 2:06 PM CDT on August 13, without a corresponding audit event. That also lines up with the issue disappearing.
This looks like a temporary backend provisioning problem where new mailboxes ignored their assigned mailbox plan defaults. Has anyone else encountered this, particularly in environments using Entra Cloud Sync or in the NAMPR04 region? Was there a service health notification, and did Microsoft provide any remediation guidance?
4 Answers
A coworker audited a similar batch of affected mailboxes and found no customer-side operation responsible. The behavior appeared limited to mailboxes provisioned during a short window, and newer mailboxes began receiving the correct limits once the backend issue was resolved.
We also had several users receive 50 KB send and receive limits. We have not found any administrative changes or synchronization attributes that explain it, so a backend change seems likely.
We saw a few mailboxes provision with extremely small limits too, including around 2 MB. It looked much more like a Microsoft-side provisioning or default-value problem than anything in the licensing configuration.
Yes, there was a service health notice describing an incident where initial mailbox settings were not being applied correctly and configured defaults were ignored for a period of time. The incident was marked resolved, but mailboxes created during the affected window still needed to be checked and corrected manually.
I found the incident history after searching the service health records. It specifically mentioned newly provisioned mailboxes and manual remediation for objects that were created while the issue was active.
To clarify, the 50 KB value was the send and receive limit, not the mailbox storage quota. Manually setting both parameters fixed the affected accounts.