I couldn't find any appropriate step by step guide for changing HELO header values in Exchange 2010.
The problem is that the server doesn't allow changing the Default FQDN in: EMC -> Server configuration -> Hub transport -> Receive Connectors -> Default entry. The problem comes from the reason it is Default. I've read that I have to use Power Shell to change it. If someone knows the correct commands to change this in Exchange 2010 I'd be rather thankful for this major help.
Regards!