OS27 mail crashes at launch of app

Because there is limited technical information provided, and no previous troubleshooting steps are mentioned, the specific cause of the Mail crash cannot yet be determined. 

The suggestions below are based on information and procedures documented by Apple Support or Apple Developer Documentation.

First, how many times has the Mac been restarted since upgrading to macOS 27.0 Golden Gate? 

Also, does Mail still crash when the Mac is started in Safe Mode? 

Apple says Safe Mode can help determine whether a problem is caused by software that loads when the Mac starts.

Apple’s macOS 27 release notes do not currently list Mail crashing at launch as a documented issue. 

They do identify a separate Mail issue involving Smart Mailboxes not updating. Apple macOS 27 Release Notes

If Mail opens normally in Safe Mode but crashes during a normal startup, that gives us a useful direction for further troubleshooting. 

If it crashes in both modes, the Mail crash report becomes especially useful. 

Apple’s general guidance for apps that unexpectedly quit includes checking for software updates and compatibility and considering third-party software that may affect the app. Apple Support: If an app freezes or quits unexpectedly on Mac

To identify the specific cause, open Console > Crash Reports and find the most recent Mail crash report. 

Without that report, identifying macOS 27.0, Mail data, an email account, or third-party software as the cause would be speculative.