Outage in HubSpot
Intermittent DMARC failures for messages to Microsoft-hosted inboxes
Resolved MinorIncident Report
Summary AI Generated
HubSpot customers experienced intermittent DMARC failures when sending emails to Microsoft-hosted inboxes, with the most significant impact affecting senders who had DMARC policies set to reject or quarantine messages. The issue was caused by improper handling of certain email headers. HubSpot implemented a fix and resolved the incident after 27.7 hours, though some delayed deliveries continued for up to 48 hours as email queues cleared.
In April, some customers may have experienced intermittent DMARC failures on messages to Microsoft-hosted inboxes. Impact was most visible for senders with a DMARC policy of p=reject or p=quarantine. The root cause was related to how certain email headers were being handled.
We have implemented a fix and will continue to monitor closely. While there may still be some residual impact to messages as outstanding retries and queue delays clear over the next ~72 hours, we expect impact to remain limited.
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Latest Updates ( sorted recent to last )
RESOLVED
about 20 hours ago - at 05/02/2026 07:31PM
HubSpot has continued to monitor the fix and believe we have addressed the underlying issue. Some messages deployed before May 1, 5 pm EDT may still experience delayed deliveries or failures over the next ~48 hours as retries and queues fully clear.
MONITORING
2 days ago - at 05/01/2026 04:34PM
In April, some customers may have experienced intermittent DMARC failures on messages to Microsoft-hosted inboxes. Impact was most visible for senders with a DMARC policy of p=reject or p=quarantine. The root cause was related to how certain email headers were being handled.
We have implemented a fix and will continue to monitor closely. While there may still be some residual impact to messages with elongated headers and as outstanding retries and queue delays clear over the next ~72 hours, we expect impact to remain limited.
MONITORING
2 days ago - at 05/01/2026 03:52PM
In April, some customers may have experienced intermittent DMARC failures on messages to Microsoft-hosted inboxes. Impact was most visible for senders with a DMARC policy of p=reject or p=quarantine. The root cause was related to how certain email headers were being handled.
We have implemented a fix and will continue to monitor closely. While there may still be some residual impact to messages as outstanding retries and queue delays clear over the next ~72 hours, we expect impact to remain limited.
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