Fastmail - Microsoft update misclassifying Fastmail emails to Outlook addresses – Incident details

All systems operational

Microsoft update misclassifying Fastmail emails to Outlook addresses

Resolved
Degraded performance
Started 6 months agoLasted about 1 month

Affected

Mail delivery

Operational from 4:30 AM to 5:23 AM

Updates
  • Resolved
    UTC
    Resolved

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

  • Monitoring
    UTC
    Monitoring

    The deliverability issues affecting emails sent to Outlook-hosted addresses have stabilized. We are continuing to monitor.

  • Identified
    UTC
    Identified

    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
    UTC
    Monitoring

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

  • Identified
    UTC
    Identified

    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. 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.