Has anyone else seen newly provisioned Exchange Online mailboxes inherit incorrect MaxSendSize and MaxReceiveSize values? In our tenant, 79 of 169 mailboxes created during a 30-day period were affected. Mailboxes provisioned from July 30 through August 7 received 35 MB send and 36 MB receive 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 using the expected 150 MB values again.
Our environment uses Entra Cloud Sync with users sourced from on-premises Active Directory, but Exchange is fully cloud-hosted. The affected mailboxes included regular users, shared mailboxes, and service accounts across multiple license types. All mailbox plans are configured for 150 MB, and there is no on-premises Exchange installation or synchronized Exchange size attributes.
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. Manually correcting an affected mailbox with Set-Mailbox persists successfully. Interestingly, all four mailbox plans show nearly identical modification timestamps on August 13, despite no matching administrative audit events.
This looks like a temporary Microsoft-side provisioning issue in which new mailboxes ignored their assigned mailbox plan. Has anyone else encountered this, received a service health notification, or identified a regional or provisioning-related pattern?
4 Answers
A couple of users in our environment had the same issue recently. We reviewed the licensing, mailbox plans, and administrative changes but couldn’t find anything that would have set those values. The likely explanation was a temporary service-side provisioning problem.
There was a service health notice describing an incident where initial mailbox settings were not 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 required manual correction.
We also found a few mailboxes with 50 KB send and receive limits. We haven’t identified a customer-side cause, and the behavior appeared to be related to a Microsoft backend change.
We saw a similar problem, including some mailboxes provisioned with extremely small limits—around 2 MB. It looked like a backend provisioning error rather than anything in the licensing or directory configuration.
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