Hello,
So after checking logs and processes, we are confident that ARCHICAD does not share any function or component with Mail app, so the chances of ARCHICAD crashing Mail app are rather slim.
The work email used for accessing licenses, is just for credentials (email and password) on GRAPHISOFT services. These credentials are (should be) different from the credentials used for accessing the email account in Mail app. ARCHICAD or any other GRAPHISOFT product does not request access to any email account.
I assume Apple support already suggested to run Mail app from another account on that machine. If the Mail app runs fine with a different user, then the issue is with user data on that user profile. On the off-chance they did not recommend that, I would kindly ask of you to test this and let me know of the results.
Kind regards,
Ghaleb & Technical Support Team