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Microsoft Exchange Online classic Outlook connectivity outage

Service Disruption
First reported
Last updated
Happening score
H score 25
1 unique sources, 1 articles

Summary

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Microsoft's Exchange Online outage is preventing classic Outlook users from connecting to mailboxes, disrupting access for customers in Asia Pacific and North America. The incident was acknowledged at 09:57 AM UTC and is being investigated as a service-side connectivity failure. Microsoft says the current workaround is to use Outlook on the Web until the issue is mitigated.

Related Happenings

Microsoft Exchange CVE-2026-42897 mitigation advisory

Advisory/Mitigation
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

Microsoft Exchange Server spoofing/XSS flaw under active exploitation (CVE-2026-42897)

Vulnerability
First: 15.05.2026 09:19 Last: 15.05.2026 09:19 Sources 1

About this happening: **CVE-2026-42897** is an **actively exploited** **spoofing/XSS** flaw in **on-premises Microsoft Exchange Server** that can let attackers trigger **arbitrary JavaScript** in a bro...

Open Happening

Microsoft Windows 365 Office installation disruption

Service Disruption
First: 13.05.2026 14:53 Last: 13.05.2026 14:53 Sources 1

About this happening: The **Windows 365** service update has introduced a **configuration change** that is blocking **Office downloads and installs** for some customers, disrupting access on cloud PCs....

Open Happening

Microsoft Exchange Online blocks legacy TLS for POP3 and IMAP4 starting July 2026

Security Tool/Service
First: 28.04.2026 16:18 Last: 28.04.2026 16:18 Sources 1

About this happening: **Microsoft** will block **TLS 1.0** and **TLS 1.1** for **POP3/IMAP4** access to **Exchange Online** in **July 2026**, which could break legacy mail clients and embedded devices...

Open Happening

Microsoft Outlook.com outage causing sign-in failures

Service Disruption
First: 27.04.2026 15:03 Last: 27.04.2026 15:03 Sources 1

About this happening: Microsoft's **Outlook.com** is experiencing an **ongoing outage** that is blocking sign-ins and mailbox access, leaving some customers unable to use email normally. The disruption...

Open Happening

Timeline

  1. 25.11.2025 11:57 2 articles · 6mo ago

    Microsoft acknowledges Exchange Online mailbox connectivity outage in classic Outlook

    Initial Disclosure

    Microsoft acknowledged an Exchange Online service incident, EX1189820, that is preventing some users from connecting to their Exchange Online mailbox through the classic Outlook desktop client. Impact is limited to users in Asia Pacific and North America, and affected customers are advised to use Outlook on the Web while Microsoft investigates the connectivity failures and related login and server connection issues.

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