Summary

On November 11, 2026, some Kustomer customers were unable to send or schedule outbound emails from approximately 15:57 to 16:50 UTC, lasting about 1 hour. The incident is resolved. Outbound email sending has returned to normal.

Impact

Agents in organizations that use conversation Brands, and had not yet mapped Brands to their sending email addresses, received errors when sending or scheduling outbound email. Organizations without Brands, and channels other than email, were not affected. Messages were rejected rather than silently dropped, and no data loss is expected.

Timeline

All times are UTC on November 11, 2026.

• 15:57: A release containing a change to outbound email sender validation reached PROD2 and PROD4. Affected customers began seeing send failures.
• ~16:10: Customer and internal reports of send failures were received, and the team began rolling back the release.
• 16:50: The rollback was complete, and outbound email sending was restored for all affected customers.

Root Cause

A change to outbound email validation, which checks that the “From” address belongs to the conversation’s Brand, was enabled for all organizations. Organizations that had set Brands on conversations but had not yet mapped Brands to email addresses failed this check, even when sending from addresses that had previously worked. The change was released before customers had been notified of, and given time to complete, the required Brand-to-email address setup.

Resolution

We rolled back the release to its previous version, which restored outbound email sending. The change has been removed from the release pipeline and will not be re-enabled until the preventative actions below are complete.

Preventative Actions

Our follow-up work focuses on making sure configuration requirements are communicated before enforcement begins:

• Hold the change until customers have been notified and have had time to complete their Brand-to-email address mappings.
• Require explicit readiness criteria and a staged rollout before enforcing sender validation for all organizations.
• Evaluate a more permissive default behavior for organizations with incomplete Brand configuration, so a missing setup step does not block sending.