Microsoft Resolves Exchange Online Mailbox Quarantine Issue

Microsoft is addressing an Exchange Online incident, tracked as EX1436407, which began on July 19, 2026. The issue has caused mailboxes to be incorrectly quarantined due to excessive memory consumption from a recent infrastructure change. Affected users are unable to send or receive emails and access their calendars, resulting in non-delivery reports for external senders. As of July 23, the cleanup process is ongoing, with 72% of the excess indexing data removed. Microsoft has not disclosed the number of affected customers or the specific regions impacted. This incident is a recurrence of a previous issue, EX1434354, indicating a pattern of similar problems. Microsoft plans to provide a completion timeline in a future update.

Key Points: • Exchange Online mailboxes have been incorrectly quarantined since July 19, 2026. • The issue is linked to excessive memory consumption from a recent infrastructure change. • Microsoft is actively working on remediation, with 72% of the cleanup process completed.