After you remove a connected email account from a Microsoft Exchange Online mailbox in Microsoft Office 365, you continue to receive email messages that are sent to the connected account in the Exchange Online mailbox. Additionally, when you open the Exchange admin center, you don't see any connected accounts under Connected Accounts.
This issue occurs if the subscription object that's associated with the connected account wasn't removed or updated successfully.
To resolve this issue, check whether forwarding rules are set up on the external mail account. If rules are set up, remove them. If no rules are set up, or if the issue persists after you remove the rules, manually remove the connected account. To do this, follow these steps:
Connect to Exchange Online by using remote PowerShell. For more information about how to do this, go to the following Microsoft website: