lost emails
how to restore old emails that were lost when email account was removed from account preferences
MacBook Air 13", macOS 10.15
Quote:
Turn on accounts in System Preferences: Choose Apple menu 
> System Preferences, click Internet Accounts, select an account, then select the Mail checkbox.
https://support.apple.com/guide/mail/if-an-email-account-is-inactive-mlhlp1207/mac