KnowBe4 incident
Prevent and Protect - Web Add-in Send Issues (EU Only)
Resolved after 4 hours 54 minutes, affecting Web Add-In and Web Add-In, on October 13, 2026.
From Monday, October 12, 2026, at approximately 14:25 \(UTC\), to Tuesday, October 13, 2026, at around 15:07 \(UTC\), some customers in EU instances of Prevent and Protect had difficulty sending emails from Microsoft Outlook. Affected messages weren't sent, and the KnowBe4 Email Security add-in displayed the following error: "The add-in KnowBe4 Email Security is preventing this message from being sent." This issue was caused by an error in how an add-in version was prepared for release, which produced two slightly different copies of the same version. When Outlook loads the add-in, it downloads a set of files that must match. In EU instances, Outlook sometimes received files from both copies, so the add-in couldn't finish loading, and the message wasn't sent. Some devices also saved the failed download, so the error continued on those devices until a fix was applied. To resolve this issue, our team corrected the EU add-in files so that every customer receives a matching set. We then released an updated version of the add-in to all regions, which cleared any saved errors. The KnowBe4 Email Security add-in returned to normal performance by about 15:07 \(UTC\) on October 13, 2026. To prevent this type of issue in the future, we're changing how add-in versions are prepared and released, so that each version always produces the same set of files and every customer receives the same version at the same time. We're also changing the add-in so that failed downloads of add-in files aren't saved on devices. Lastly, we're adding alerts for add-in loading errors to detect them sooner. No data loss occurred as a result of this issue.
Affected components
Update timeline
- investigating Oct 13, 2026, 08:47 AM UTC
We have received reports that the KnowBe4 Email Security Add-in is showing the error "The add-in KnowBe4 email security is preventing this message from being sent" when sending emails. We are investigating this issue and will update this page when we have more information.
- monitoring Oct 13, 2026, 11:07 AM UTC
We’ve implemented a fix for the Web Add-in sending errors and we’re monitoring the results to make sure no further issues occur.
- resolved Oct 13, 2026, 01:41 PM UTC
This incident has been resolved.
- postmortem Oct 20, 2026, 12:48 PM UTC
From Monday, October 12, 2026, at approximately 14:25 \(UTC\), to Tuesday, October 13, 2026, at around 15:07 \(UTC\), some customers in EU instances of Prevent and Protect had difficulty sending emails from Microsoft Outlook. Affected messages weren't sent, and the KnowBe4 Email Security add-in displayed the following error: "The add-in KnowBe4 Email Security is preventing this message from being sent." This issue was caused by an error in how an add-in version was prepared for release, which produced two slightly different copies of the same version. When Outlook loads the add-in, it downloads a set of files that must match. In EU instances, Outlook sometimes received files from both copies, so the add-in couldn't finish loading, and the message wasn't sent. Some devices also saved the failed download, so the error continued on those devices until a fix was applied. To resolve this issue, our team corrected the EU add-in files so that every customer receives a matching set. We then released an updated version of the add-in to all regions, which cleared any saved errors. The KnowBe4 Email Security add-in returned to normal performance by about 15:07 \(UTC\) on October 13, 2026. To prevent this type of issue in the future, we're changing how add-in versions are prepared and released, so that each version always produces the same set of files and every customer receives the same version at the same time. We're also changing the add-in so that failed downloads of add-in files aren't saved on devices. Lastly, we're adding alerts for add-in loading errors to detect them sooner. No data loss occurred as a result of this issue.
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