Email Messages sent from O365 to OnPrem Hybrid marked as Anonymous

I was givenhttps://support.microsoft.com/en-us/help/2663556/email-messages-that-are-sent-from-the-on-premises-e...as a solution, but number 2) shows:

Check the remote domain of the on-premises Exchange server. To do this, follow these steps:In Exchange Management Shell, run the following PowerShell command:

How do I know what should be to check?

The issue: Email from those who have been Migrated to O365 are being identified as Anonymous.

X-MS-ExchangeOrganization-AuthAsAnonymous