Mail Crashing

My mail has developed a regular crash issue which I can't resolve.

I've done a Safe Boot (twice) and run the Disc Utility First Aid.

This is a from the Etrecheck report:

Diagnostics Information (past 7-30 days):

    2020-10-16 13:00:49 Mail.app - Crash (10 times)

        Executable: /Applications/Mail.app

        Details: 

            *** Terminating app due to uncaught exception 'NSRangeException', reas

            on: '*** -[__NSArrayM objectAtIndexedSubscript:]: index 92233720368547

            75807 beyond bounds [0 .. 7]'

            terminating with uncaught exception of type NSException

            abort() called

And a screen shot of part of the report sent to Apple is attached.

All help very much welcomed.