Outage in Customer.io
Reduced Deliverability to Microsoft-Hosted Email Addresses
Resolved MinorIncident Report
Summary AI Generated
Starting around 08:00 UTC on September 4, 2026, a Microsoft-side incident caused increased email deferrals and bounces for messages sent to Microsoft-hosted email addresses via Customer.io. The issue lasted approximately 1.4 hours, with no other email providers affected. Microsoft resolved the underlying problem, after which deliveries resumed normally and earlier bounced messages were queued for retry.
We are currently investigating reports of reduced deliverability affecting messages sent to Microsoft-hosted email addresses. Our team is actively looking into this and we will provide an update as soon as we have more information. Thank you for your patience!
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Latest Updates ( sorted recent to last )
RESOLVED
about 16 hours ago - at 09/04/2026 01:35PM
Microsoft has resolved the underlying issue, we are seeing deliveries to their services resume as normal. Earlier bounces will be retried accordingly. We appreciate your understanding and please do reach out to support if you need any further assistance.
MONITORING
about 17 hours ago - at 09/04/2026 12:30PM
Starting around 08:00 UTC, Microsoft began experiencing an incident causing an increased volume of deferred/bounced emails. We are actively monitoring the situation. No other email providers are currently affected.
INVESTIGATING
about 17 hours ago - at 09/04/2026 12:16PM
We are currently investigating reports of reduced deliverability affecting messages sent to Microsoft-hosted email addresses. Our team is actively looking into this and we will provide an update as soon as we have more information. Thank you for your patience!
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