Answer
PROBLEM
When email is sent from the GFI MailEssentials relay server to your domain you see in the Message Delivery Log the Status Reply:530 5.7.1 Client was not authenticated
ENVIRONMENT
- GFI MailEssentials
- All Supported Environments
SOLUTION
- Open Exchange Management Console > Server Configuration > Hub Transport > Default Receive Connector > Properties
- Click Permission Groups
- Check the box Anonymous Users
- Click Apply then OK
http://www.gfi.com/support/products/gfi-mailessentials/How-to-install-MailEssentials-on-an-SMTP-Relay