...
If you have a local archive of email files that you have manually added to your Exchange account in Apple Mail, you may need to manually reconnect those local archives again as well (see note in bold above). If you did add an additional account and would like to remove it after adding your MIT mailbox back to Apple Mail, see here for instructions on how to do so: https://support.apple.com/guide/mail/log-out-of-or-remove-email-accounts-mlhl9eb9408c/15.0/mac/13.0
...