Importing Mail Failure after a System Recovery

My late 2011 MacBook Pro's ssd failed suddenly and completely. I used my Time Machine backup to restore a new ssd. Everything on the recovered new ssd worked successfully except Mail. When I started Mail it appeared to be recovering all the mail including the folders and subfolders but at the end of the process Mail complained that there was an error, aborted and quit. I looked in Library/mail/V5 and I was able to see all the mail folders and sub folders so I know that all the mail is there and I can see thousands of EMIX files in the folders. I would like to view all the emails and save the most important emails and delete most of the unimportant emails and I would like to be able to run Mail again. At the moment Mail seems to only start and import mail (which fails) or not run at all.

The laptop is running OSX 10.13.6 which is latest OS which will run on this computer.

I would appreciate any help to recover from this disaster. Do you have experience with Apple EMIX Mail Converter? Do you know of another program that will recover the email? I don't mind purchasing a tool if I know it would work. If I can recover the messages and store them somewhere else that would be okay too.