You can easily check if you have an open relay with websites like http://www.mxtoolbox.com/, https://www.testexchangeconnectivity.com and http://www.checkor.com/ When you found out that they say that you have an open relay you can double check that with the following command : Get-ReceiveConnector | Get-ADPermission | where {($_.ExtendedRights -like “*SMTP-Accept-Any-Recipient*”)} | whereRead More →