{"id":14998,"date":"2026-02-18T07:01:37","date_gmt":"2026-02-17T22:01:37","guid":{"rendered":"https:\/\/m365jp.net\/?p=14998"},"modified":"2026-02-18T07:06:10","modified_gmt":"2026-02-17T22:06:10","slug":"servicerestored-ex1228240-exchange-online-users-mailtips-may-not-reflect-free-busy-correctly-in-outlook-desktop-and-crashes-may-occur-when-adding-mailboxes","status":"publish","type":"post","link":"https:\/\/m365jp.net\/index.php\/2026-02-18-servicerestored-ex1228240-exchange-online-users-mailtips-may-not-reflect-free-busy-correctly-in-outlook-desktop-and-crashes-may-occur-when-adding-mailboxes","title":{"rendered":"[serviceRestored] EX1228240 | Exchange Online | Users’ MailTips may not reflect free\/busy correctly in Outlook desktop and crashes may occur when adding mailboxes"},"content":{"rendered":"
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EX1228240 | Exchange Online | Users’ MailTips may not reflect free\/busy correctly in Outlook desktop and crashes may occur when adding mailboxes<\/th>\n<\/tr>\n<\/tbody>\n<\/table>\n
\n\n\n\n\n\n\n\n\n\n
Status<\/th>\nserviceRestored<\/td>\n<\/tr>\n
Classification<\/th>\nadvisory<\/td>\n<\/tr>\n
User Impact<\/th>\nUsers’ MailTips may not have reflected free\/busy correctly in Outlook desktop and crashes may have occurred.<\/td>\n<\/tr>\n
Last Updated<\/th>\n02\/17\/2026 21:08:02<\/td>\n<\/tr>\n
Start Time<\/th>\n01\/27\/2026 18:00:00<\/td>\n<\/tr>\n
End Time<\/th>\n02\/12\/2026 18:00:00<\/td>\n<\/tr>\n
Latest Message<\/th>\nTitle: Users’ MailTips may not reflect free\/busy correctly in Outlook desktop and crashes may occur when adding mailboxes<\/p>\n

User impact: Users’ MailTips may not have reflected free\/busy correctly in Outlook desktop and crashes may have occurred.<\/p>\n

More info: This issue was specific to the Outlook desktop client in organizations with a hybrid environment that used Exchange Web Services (EWS) for MailTips. Users may have noticed that the MailTips free\/busy feature wasn\u2019t operating as expected and may have seen an error stating \u201cwe can\u2019t show MailTips right now.\u201d<\/p>\n

The Outlook desktop crashes occurred when users attempted to add a new on-premises mailbox.<\/p>\n

Admins may have been unable to create new on-premises mailboxes, and their cross-tenant AutoDiscover requests general may have failed from hybrid environments.<\/p>\n

While we worked on deploying the fix, admins may have been able to mitigate the impact by restarting the Autodiscover app pool.<\/p>\n

Final status: We’ve validated with a subset of affected users that the fix to prevent the header duplication issue has fully resolved the impact.<\/p>\n

Scope of impact: Any admins\u2019 cross-tenant AutoDiscover requests may have failed from hybrid environments, which caused MailTips free\/busy not to show and crash for users\u2019 Outlook desktop clients when they added additional on-premises mailboxes.<\/p>\n

Start time: Tuesday, January 27, 2026, at 12:30 AM UTC<\/p>\n

End time: Thursday, February 12, 2026, at 6:00 PM UTC<\/p>\n

Root cause: A routing change for Autodiscover requests introduced a header duplication issue which caused a backlog of requests that ultimately failed or timed out and resulted in the impact.<\/p>\n

Next steps:
– We’re reviewing our change implementation standards to ensure similar issues are caught and addressed ahead of deployment to prevent this from happening again.<\/p>\n

This is the final update for the event.<\/td>\n<\/tr>\n<\/tbody>\n<\/table><\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"

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