Import mail messages box pops up when Mail is started, then import fails.

Hello jmccarty3,

One solution would be to close the Mail application, access System Settings > Internet Accounts and then, for each account, one by one, disable Mail for this account (it is not necessary to disable Calendar, Notes etc.). After deactivating an account, open the Mail application and see if the import proceeds without error. Then reactivate the Mail accounts that you had to deactivate.

May 2024, the problem still exists, and we just used this method to solve it. Turned out the problem was with a Google Mail Account, which we fixed via browser, and everything works fine. Thank you very much!

You are welcome.

THANK YOU! :)