Defend - Increased Email Latency (US Only)
Postmortem
Summary
On June 30, 2026, customers using the Defend US service experienced delays in email processing. The incident began at approximately 14:00 UTC and was fully resolved by 19:45 UTC.
What Happened
A scheduled maintenance operation began in the early morning of June 30. As this operation progressed, it placed an unexpectedly high load on our infrastructure, which caused email processing to slow down across our US service.
Our team identified the issue and declared an incident at 16:00 UTC. Steps were taken to reduce the load and restore normal processing speeds, including pausing non-essential background activity and engaging our infrastructure provider for additional support.
By 17:45 UTC, email delivery delays had been fully resolved. Email analysis continued to recover and was back to normal by 19:45 UTC.
Customer Impact
Email delivery (SMTP customers): Emails were delayed in transit by up to 30 minutes between approximately 14:00 UTC and 17:45 UTC. All emails were delivered; no messages were lost.
Email analysis (Microsoft 365 / Graph API customers): Email analysis was delayed by an average of 30 minutes before emails were analysed, between approximately 14:00 UTC and 19:45 UTC. Email delivery to end users was not affected.
What We Are Doing
We have rescheduled the maintenance operation that triggered this incident to run during an overnight, low-traffic window, giving it sufficient time to complete without affecting the live service.
We are also investing in infrastructure improvements to better isolate maintenance operations from customer-facing workloads, so that future maintenance cannot affect email processing in this way.