M365 Add-In: Silently failing checks for a subset of users

Impact window: 10:03 UTC - 13:08 UTC December 2nd 2025 Impacted Add-in: Smart Alerts M365 Add-in Impacted Mail Client: Classic Outlook For any end users who started Classic Outlook during the impact window (10:03 UTC - 13:08 UTC), who have the Smart Alerts M365 Add-in deployed, Outbound checks via the Add-in will fail silently. At 13:08 UTC - Proofpoint rolled back to the last known good version on our backend - mitigating the issue. However, end users who opened Classic Outlook between 10:03 UTC and 13:08 UTC will still have the bad configuration cached, and will not be able to take advantage of the fix until their Outlook restarts and pulls down the newest configuration. There is no impact to users still on the Legacy version of the M365 Add-in, or using New Outlook or OWA mail clients with Smart Alerts to send emails. Customers configured to use the Outbound Gateway as a backup will still have mail routed and checked by the gateway if the M365 Add-in failed to check. Proofpoint will continue to monitor closely for the next 24 hours to ensure all operations remain stable.