Fastmail incident

Microsoft update misclassifying Fastmail emails to Outlook addresses

Minor Resolved View vendor source →

Fastmail experienced a minor incident on January 27, 2026, lasting 34d. The incident has been resolved; the full update timeline is below.

Started
Jan 27, 2026, 04:30 AM UTC
Resolved
Mar 02, 2026, 05:23 AM UTC
Duration
34d
Detected by Pingoru
Jan 27, 2026, 04:30 AM UTC

Update timeline

  1. 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..

  2. monitoring Feb 05, 2026, 12:00 PM UTC

    Microsoft has addressed this issue and we believe the is now resolved. We continue to monitor..

  3. 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..

  4. 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..

  5. resolved Mar 02, 2026, 05:23 AM UTC

    The deliverability issues to Outlook-hosted email addresses are now resolved..