Use Google Cloud Directory Sync to synchronize your local identity management system to Cloud Identity.

Use the Google Admin console to view which managed users are using a personal account for their recovery email.

Add users to your managed Google account and force users to change the email addresses associated with their personal accounts.

Use the Transfer Tool for Unmanaged Users (TTUU) to find users with conflicting accounts and ask them to transfer their personal Google accounts.

Send an email to all of your employees and ask those users with corporate email addresses for personal Google accounts to delete the personal accounts immediately.