Find notable cyber news and cases, enriched with sources, timelines, and signals.
Home Browse News Feed Stats Watchlists Beta About Contact

Microsoft Exchange Online Outlook mobile sync disruption

Service Disruption
First reported
Last updated
Happening score
H score 13
1 unique sources, 1 articles

Summary

Hide ▲

The Microsoft Exchange Online disruption is delaying mail syncs for Outlook mobile users who use Hybrid Modern Authentication (HMA), leaving some customers unable to access email and calendars. The problem began on August 17 and caused some users to be unable to send or receive email. A recent service change triggered 12-hour sync delays, and a fix has been deployed, but the issue was still being tracked as ongoing at publication.

Related Happenings

Microsoft Exchange Online email quarantine disruption

Service Disruption
First: 09.02.2026 12:47 Last: 09.02.2026 12:47 Sources 1

About this happening: Microsoft's **Exchange Online** is facing an ongoing **email delivery disruption** that is **quarantining legitimate messages** and blocking some customers from **sending or recei...

Latest development: 18.02.2026 18:26

Microsoft’s preliminary post-incident report for Exchange Online says a logic error in heuristic detection aimed at novel credential phishing campaigns misclassified thousands of legitimate URLs as phishing links, quarantined legitimate emails, blocked links in Microsoft Teams messages, and generated false-positive XDR alerts during the February 5-12 incident window.

Open Happening

Microsoft Teams messaging delay outage

Service Disruption
First: 19.12.2025 22:04 Last: 19.12.2025 22:04 Sources 1

About this happening: **Microsoft Teams** is experiencing **messaging delays** and related service-function issues, disrupting communication for **thousands of users** across **all regions**, including...

Open Happening

Exchange Online Exchange ActiveSync 16.1 cutoff

Advisory/Mitigation
First: 16.12.2025 14:53 Last: 16.12.2025 14:53 Sources 1

About this happening: **Microsoft** will block **Exchange Online** access for **Exchange ActiveSync** devices below **16.1**, forcing administrators to update legacy mobile email clients before **March...

Open Happening

Microsoft new Outlook Excel attachment opening issue

Service Disruption
First: 01.12.2025 19:42 Last: 01.12.2025 19:42 Sources 1

About this happening: The **new Outlook client** is experiencing a **service disruption** that can block users from opening **Excel email attachments**, interrupting routine file access. The issue has...

Open Happening

Microsoft Exchange Online classic Outlook connectivity outage

Service Disruption
First: 25.11.2025 18:18 Last: 25.11.2025 18:18 Sources 1

About this happening: Microsoft's **Exchange Online** outage is preventing **classic Outlook** users from connecting to mailboxes, disrupting access for customers in **Asia Pacific** and **North Americ...

Open Happening

Timeline

  1. 23.08.2025 17:15 1 articles · 9mo ago

    Outlook mobile HMA users hit by Exchange Online sync delays

    Victim Impact Update

    Microsoft Exchange Online users on Outlook mobile with Hybrid Modern Authentication began experiencing email access problems on August 17, 2025, when a recent service change triggered 12-hour sync delays. Some mailboxes crashed, and affected customers could not send or receive email or access calendars.

    Show sources
    Open in new tab
  2. 23.08.2025 17:15 1 articles · 9mo ago

    Microsoft deploys fix for Exchange Online sync quarantine issue

    Mitigation Patch Update

    On August 23, 2025, Microsoft said engineers had deployed a fix for the Exchange Online Outlook mobile issue by preventing sync jobs from entering the quarantine state. A previous configuration change intended to shorten the delay to one hour had not succeeded, and the service issue was still being treated as an incident with ongoing customer impact at publication.

    Show sources
    Open in new tab