Fastmail incident
Microsoft update misclassifying Fastmail emails to Outlook addresses
Resolved after 34 days, on January 27, 2026.
The deliverability issues affecting emails sent to Outlook-hosted addresses have stabilized. We are continuing to monitor..
Update timeline
- identified Jan 27, 2026, 04:30 AM UTC
A recent Microsoft update is sometimes incorrectly flagging some emails from several providers, including Fastmail. This is causing intermittent delivery issues for some email sent to addresses hosted on [outlook.com](http://outlook.com). We are seeing a small percentage of outgoing mail affected, with no obvious reason as to why. Our team is actively working with Microsoft's email team to get this resolved as soon as possible..
- monitoring Feb 05, 2026, 12:00 PM UTC
Microsoft has addressed this issue and we believe the is now resolved. We continue to monitor..
- identified Feb 13, 2026, 08:30 PM UTC
We’ve noticed that a small percentage of emails sent to Outlook-hosted addresses are being affected again. We’re in touch with Microsoft and working with them to resolve it..
- monitoring Feb 18, 2026, 05:29 AM UTC
The deliverability issues affecting emails sent to Outlook-hosted addresses have stabilized. We are continuing to monitor..
- resolved Mar 02, 2026, 05:23 AM UTC
The deliverability issues to Outlook-hosted email addresses are now resolved..
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