How to Reconnect to Exchange post Migration
From Help Wiki
Once your mailbox has been migrated to Exchange Online you may need to reconnect your mail clients to the Exchange service to update your settings.
- Disconnect your old account from the mail client
- Reconnect using the Exchange account connector
Mac OS
Disconnect Exchange Account - Mac OS
- Go to System Preferences > Internet Accounts
- Select your old Exchange connector on the left had column
- Click the "-" the minus sign to remove
Reconnect Exchange Account - MacOS
iOS
Disconnect Exchange Account - iOS
- Go to Settings > Passwords & Accounts
- Under the list of Accounts Select your old Exchange account
- Choose Delete Account