Outage in Hornetsecurity
External Incident – Microsoft Service Degradation of Outlook Add-ins
Resolved Minor
March 26, 2026 - Started 26 days ago
- Lasted 6 days
Incident Report
Summary AI Generated
Microsoft experienced a service degradation (incident EX1259460) that prevented some users from accessing custom Outlook add-ins through Exchange Online connections, affecting Hornetsecurity's 365 Total Protection service. The incident lasted 141.6 hours and was caused by authentication-related issues and traffic load balancing problems in Microsoft's environment. Hornetsecurity provided manual installation workarounds for their Total Protection and AIRV Outlook add-ins while Microsoft investigated the root cause.
Microsoft incident reference: EX1259460
Issue Description: Some users may be unable to access custom add-ins through any Exchange Online connection method.
Latest updates from Microsoft:
26/03/2026 9:04:00 PM – Microsoft is investigating the possibility that incoming traffic may not be appropriately balanced throughout the affected environment while also continuing to review the previously identified exception to determine the root cause and a strategy that remediates impact.
25/03/2026 8:35:00 AM – Microsoft hasn't confirmed a viable workaround, however they have identified an authentication-related exception which may be contributing to the impact, and they are further reviewing this exception to aid in their root cause analysis.
Should you wish to follow updates from Microsoft directly you may do so from the Microsoft Service Health Dashboard under ID EX1259460
https://learn.microsoft.com/en-us/microsoft-365/admin/manage/health-dashboard-overview
If you are impacted by this and are unable to wait for a resolution from Microsoft, you may find available workarounds as below:
Total Protection Outlook Add-in Workaround
http://support.hornetsecurity.com/hc/en-us/articles/21797951259537-Manual-installation-of-the-Outlook-add-in
AIRV Outlook Add-in Workaround
http://cp.hornetsecurity.com/manual/en/ai_recipient_validation/t_deploy_ai_recipient_validation_add_in_manually.html
Issue Description: Some users may be unable to access custom add-ins through any Exchange Online connection method.
Latest updates from Microsoft:
26/03/2026 9:04:00 PM – Microsoft is investigating the possibility that incoming traffic may not be appropriately balanced throughout the affected environment while also continuing to review the previously identified exception to determine the root cause and a strategy that remediates impact.
25/03/2026 8:35:00 AM – Microsoft hasn't confirmed a viable workaround, however they have identified an authentication-related exception which may be contributing to the impact, and they are further reviewing this exception to aid in their root cause analysis.
Should you wish to follow updates from Microsoft directly you may do so from the Microsoft Service Health Dashboard under ID EX1259460
https://learn.microsoft.com/en-us/microsoft-365/admin/manage/health-dashboard-overview
If you are impacted by this and are unable to wait for a resolution from Microsoft, you may find available workarounds as below:
Total Protection Outlook Add-in Workaround
http://support.hornetsecurity.com/hc/en-us/articles/21797951259537-Manual-installation-of-the-Outlook-add-in
AIRV Outlook Add-in Workaround
http://cp.hornetsecurity.com/manual/en/ai_recipient_validation/t_deploy_ai_recipient_validation_add_in_manually.html
Components affected
Hornetsecurity 365 Total ProtectionTrusted by 1,000+ teams
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Latest Updates ( sorted recent to last )
26 days ago - at 03/26/2026 11:05AM
Microsoft incident reference: EX1259460
Issue Description: Some users may be unable to access custom add-ins through any Exchange Online connection method.
Latest updates from Microsoft:
26/03/2026 9:04:00 PM – Microsoft is investigating the possibility that incoming traffic may not be appropriately balanced throughout the affected environment while also continuing to review the previously identified exception to determine the root cause and a strategy that remediates impact.
25/03/2026 8:35:00 AM – Microsoft hasn't confirmed a viable workaround, however they have identified an authentication-related exception which may be contributing to the impact, and they are further reviewing this exception to aid in their root cause analysis.
Should you wish to follow updates from Microsoft directly you may do so from the Microsoft Service Health Dashboard under ID EX1259460
https://learn.microsoft.com/en-us/microsoft-365/admin/manage/health-dashboard-overview
If you are impacted by this and are unable to wait for a resolution from Microsoft, you may find available workarounds as below:
Total Protection Outlook Add-in Workaround
http://support.hornetsecurity.com/hc/en-us/articles/21797951259537-Manual-installation-of-the-Outlook-add-in
AIRV Outlook Add-in Workaround
http://cp.hornetsecurity.com/manual/en/ai_recipient_validation/t_deploy_ai_recipient_validation_add_in_manually.html
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