Unable to import mail messages after updating to Catalina
I upgraded to Catalina from High Sierra. When I opened Mail, it told me it had to import the messages. After a large number of messages imported, it stopped importing and the number on the screen remained static. On the chance that it's a space issue, began archiving large and older files to an external drive. I pulled up system information and I see that there is a Mail file showing as being 269.87GB. I cannot find this file anywhere on my HD and it appears that it is causing the space issue. My HD is 512GB and I'm currently showing 90.37GB available.
Is there a way to remove that large Mail file and re-import Mail? Can I do a backup from my Time Machine to revert to before the upgrade. (When I entered Time Machine, it was only letting me see today - I tried to go back to Tuesday or Wednesday and it wouldn't let me.)
Help is greatly appreciated.