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Microsoft Exchange Online mailbox quarantine disruption after infrastructure change

Service Disruption
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Last updated
Happening score
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1 unique sources, 1 articles

Summary

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A Microsoft Exchange Online service disruption is mistakenly quarantining customer mailboxes, blocking email delivery and calendar access for affected users. The issue is tracked as EX1436407 and began on July 19. Microsoft tied the problem to a recent infrastructure change that caused excessive memory consumption and an out-of-memory condition. Remediation is underway, with mailboxes being removed from quarantine as cleanup progresses.

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Microsoft security patch release for CVE-2026-42897

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H score44 First: 10.06.2026 16:44 Last: 10.06.2026 16:44 Sources 1

About this happening: Microsoft released June 2026 Security Updates for Exchange Server 2016, Exchange Server 2019, and Exchange Server Subscription Edition (SE) to fix CVE-2026-4...

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Microsoft security patch release for CVE-2026-45586

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Microsoft Teams and Office for the web file-opening outage

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Microsoft Exchange CVE-2026-42897 mitigation advisory

Advisory/Mitigation
H score44 First: 15.05.2026 12:40 Last: 15.05.2026 12:40 Sources 1

About this happening: Microsoft issued immediate mitigation guidance for CVE-2026-42897, reducing risk for Exchange Server 2016, 2019, and Subscription Edition (SE) on-premises servers that...

Latest development: 15.05.2026 15:35

Microsoft issued temporary mitigation guidance for CVE-2026-42897 while a patch is still in development, recommending the Exchange Emergency Mitigation (EM) Service, which is enabled by default and can be checked with the Exchange Health Checker script, or the Exchange On-premises Mitigation Tool (EOMT) for disconnected or air-gapped environments. Microsoft noted that the mitigations can disrupt features such as OWA Print Calendar and Inline images, and that servers older than March 2023 cannot receive new mitigations through EM Service.

Open Happening

Timeline

  1. 23.07.2026 12:20 2 articles · 0h ago

    Microsoft Exchange Online mailbox quarantine disruption after infrastructure change

    Initial Disclosure

    An Exchange Online mailbox quarantine problem surfaced on July 19 and quickly affected users’ ability to send and receive email and access calendars. Microsoft identified a recent infrastructure change as the trigger and began cleanup to restore quarantined mailboxes.

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