When I check the message headers of an email, I see text such as this:
Received: from mail.mydomain.net ([126.96.36.199]) by bay0-mc5-f6.bay0.hotmail.com
How are these values worked out? I expect Hotmail knows the IP. 188.8.131.52, that is connecting to it, but how about the hostname, mail.mydomain.net? Is that what is mentioned in the EHLO, or does the Hotmail server carry out a reverse DNS check on that IP address?