Microsoft Investigates Exchange Online Mailbox Quarantine Issue

The Exchange Online mailbox issue is incorrectly quarantining some customer mailboxes, preventing affected users from receiving email and accessing other services.

Microsoft is investigating the incident under EX1436407. The problem began on July 19 and remained unresolved in the company’s latest update.

Exchange Online Users May Be Unable to Receive Emails

Affected users may experience several issues, including being unable to receive new emails, getting Non-Delivery Reports when messages are sent to quarantined mailboxes, problems sending emails, and difficulty accessing calendars.

Microsoft has classified the problem as an incident, which indicates noticeable service disruption for affected customers.

Infrastructure Change Triggered the Mailbox Quarantines

Microsoft linked the issue to a recent infrastructure change.

Unexpected indexing data caused excessive memory consumption. The resulting out-of-memory condition then triggered incorrect mailbox quarantines.

The company says the current problem is a recurrence of an earlier incident tracked as EX1434354. Microsoft requires additional remediation work to restore affected services fully.

Microsoft Continues Cleaning Up Indexing Data

Microsoft is removing the excess indexing data responsible for the memory problems.

Cleanup progress reached 72% on Wednesday. The company is gradually removing mailboxes from quarantine as it validates memory levels across affected regions.

Microsoft has not disclosed how many customers or regions the incident affects. It has also provided no estimated completion time.

The incident comes shortly after Microsoft released new Extended Security Updates for Exchange Server 2016 and 2019.

In other news, Microsoft will end Exchange Server 2016 and 2019 security updates in October.

Via BleepingComputer