Mail quitting unexpectedly

1 - Suggest restarting in Safe Mode. This will perform a Disk Repair, clear cache files and only load Apple Software, extensions and fonts. The boot up will be slow and can take some time - Normal.

2 - Does the issue present in this mode ?

3 - Sometimes a Safe Boot followed by a Normal Boot will just put things right.

4 - If not - there could be something in the main User Account playing up. To further isolate this - Set up users, guests, and groups on Mac. Then log out of the Main User account and log into the dummy account and test again if the issue persists.

5 - If the issue is present in the dummy account - then, this appears to be a System Wide issue on the computer.

6 - If after performing each of the above steps is the order that have been presents  and still have issues - please advise for possible further assistance.

Understand, we are all working Remotely from all around the world. Therefore, we do not have the On-Hands experience the User ( you ) has with this computer.

The next best thing for us to having an actual On-Hand experience on this computer is to follow the steps below

Download the Application Etrecheck directly from a well Respected ASC Contributor. And Safe to use.

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.

I don't see anything glaring on these reports...don't know if I need to purchase the "power user" package for further information. In the meantime, I'm using two profiles: the dummy for mail and mine for everything else. Seems contrary to Apple ID purpose lol. Any insight is greatly appreciated.

There is nothing Specific in this report to indicate why Apple Mail would crash.

Though, there are several crashes of other Applications including some System Process too.

Apart from the fact this computer is running a Fusion Drive.

No matter how clean the Operating System may be, Fusion Drives on Modern Operating System tends to be not a swift, responsive or Performance wise as good as an All SSD Drive setup.

The user ( you ) may consider doing a Reinstallation from Recovery Mode. It would be just replacing any corrupted or missing System Elements without touching the existing preferences, setup, installed Application or personal Data.

It would be highly suggest getting a larger External Drive and perform a TM Backup Before attempting this.

I have this same issue. Mail works on dummy account, other user, webmail, and all other devices; but not in safe mode or in original admin account.

Just having a look now when your second reply arrived.

Will get back to you soon.

Thank you, i'll try that next.