mac mail crashing

Open  (Apple menu) > System Preferences... > Internet Accounts. You can temporarily turn off that account by de-selecting Mail.

To remove the account from your Mac entirely, select the affected account and click the [—] (minus) button. You can always add it again by following these instructions: Add or remove email accounts in Mail on Mac - Apple Support.

In that manner, you should be able to open Mail without it crashing, enabling you to back up or otherwise move email messages to local Mailboxes. To identify and remove an email message causing Mail to crash, use the affected email account's webmail interface, assuming it has one.

I had this problem, or one like it. An address exception, I have four mail accounts and the problem only occurred with one.

The problem has largely resolved itself, I left the mail application running with the display pointed at an account which was not causing issue. I noticed the advices coming up on the screen to tell me mail had been received for the problem account. If I tried to search the mail on that account it would crash. This suggest to me that there was a data corruption somewhere in the mailbox, but I could not isolate which message.

As the messages built up the crashes became less and less (unless I searched).

It is now operating almost normally.