mail application crashes upon opening

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Are there any AntiVirus, Disk Cleaner, Optimizers, Un-installers, etc installed which should be removed as per Developers Instructions. They are useless, unneeded, cause havoc and interfere with the normal  operation of the OS and may even Corrupt the OS requiring a Reinstallation

And CleanMyMac will fail in above category if installed and used https://discussions.apple.com/search?q=cleanmymac

Suggest downloading the Application Etrecheck directly from a well Respected ASC Contributor. 

Disclaimer: I am not affiliated with nor receive compensation from the Developer.

The application is free or paid from added features. 

Run the application with Full Disc Access ( Security & Privacy - Full Disc Access ).

It will take a Snap Shot -  both the hardware and software.

 The Report will Not Reveal Any Personal Information. 

Post back the Full Report - copy and paste - using the Additional Text Icon ( 3rd Icon to last )

We can have a look at the report for possible issues and may have possible suggestions to resolve the issues.

Any Third Party Applications that will interfere with the normal operation of the OS, alter, modify, remove or delete or attempt to do so is an invitation for disaster and may require a Reinstallation of the OS.

This includes AntiVirus, Disk Cleaners, Disk Optimizes, UnInstaller etc.

The The Built in Security  is all that is required.

Nice one " fall "

Yes - CleanMyMac - if one takes the time to read the supplied info will do things that may require the application to be Removed As Per the Developers Instruction. Then perform a Wipe and Clean install to put the OS right.

To get a real insight of what the issue is with this computer is run Etrecheck application and post the Full Report

We thank you for getting back to us with the Etrecheck Report.

That which is in Bold below, are probably the source of all the computer issues including the Apple Mail Application crashing.

Without a long lecture which as already been outlined in an earlier reply, really suggest Removing the Offending Applications as per Developers Specific Instructions.

Then - re-run the Etrecheck Application again so to check all bits and pieces of those applications are totally removed.

More than one antivirus app - This computer has multiple antivirus apps installed.

Antivirus software: Apple, CleanMyMac, and F-Secure

com.macpaw.clearvpn.macos-site-ver.system-network-extension

Test to see if the same happens in Safe Mode.

Then restart normally, download and run Etrecheck and post its full report here, using the "additional text" button below your message.