Microsoft is working to fix a bug causing Outlook to become unresponsive on the startup screen for a while before launching normally. The company acknowledged the issue in a support document published on June 19.
According to Microsoft, the Outlook desktop app syncs the entire offline data file (.ost) during the startup process. “Investigation of profile and OST file names will show new OST files are not being created (this would also appear in the Application Event Logs if it were the cause). Customers often report that if they cancel Outlook opening and try again, it will open up without delay,” Microsoft explained.
Microsoft also mentioned that the Outlook app fails to start in some instances when the Airplane mode is enabled on systems. Users will see the following error message “Cannot start Microsoft Outlook. Cannot open the Outlook window. The set of folders cannot be opened. The attempt to log on to Microsoft Exchange has failed.”
Microsoft found that the Outlook startup issues could be caused by cache re-priming. It’s a process where the cache is refreshed with the data that was previously evicted. Its purpose is to ensure faster access to that data in the future. Cache re-priming occurs when users create new profiles or disable shared calendar improvements.
Microsoft is currently working on a permanent fix for these Outlook startup issues. The company says that the problem happens when the app fails to determine the default state of the cache. As a workaround, Microsoft recommends configuring a group policy to enable the Outlook calendar sharing updates. You can find more details on the aforementioned support page.
In related news, Microsoft announced its plans to replace the Mail and Calendar apps with the web-based Outlook for Windows client on new Windows 11 devices in September 2024. However, the company has since backtracked the move citing that it’s rethinking this implementation plan.