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Microsoft classic Outlook Gmail and Yahoo sync disruption

Service Disruption
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1 unique sources, 1 articles

Summary

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The classic Outlook synchronization failure affecting Gmail and Yahoo accounts has been fixed, restoring email access for impacted users. Microsoft said the bug produced 0x800CCC0F and 0x80070057 errors and stopped some accounts from signing in normally. The fix landed in the Microsoft 365 service, though some customers may still need to wait for OAuth token expiry or use a registry workaround.

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 Defender false-positively flags DigiCert root certificates and removes some from Windows trust store

Security Tool/Service
First: 03.05.2026 21:11 Last: 03.05.2026 21:11 Sources 1

About this happening: **Microsoft Defender** began falsely flagging valid **DigiCert root certificates** as **Trojan:Win32/Cerdigent.A!dha**, creating widespread false positives and risking certificate...

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

Timeline

  1. 24.03.2026 17:12 1 articles · 2mo ago

    Classic Outlook Gmail and Yahoo sync disruption begins

    Victim Impact Update

    Classic Outlook users syncing Gmail and Yahoo accounts lost normal mail synchronization, with Microsoft saying the affected accounts stopped syncing on February 26, 2026 and Outlook no longer prompted users to sign in when sync failed.

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  2. 24.03.2026 17:12 2 articles · 2mo ago

    Microsoft fixes classic Outlook sync bug and shares workaround

    Mitigation Patch Update

    Microsoft fixed the classic Outlook synchronization bug in the Microsoft 365 service and said some affected users may still need to wait for OAuth token expiry or use the registry workaround under Computer\HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity\Identities to force the Outlook sign-in prompt.

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