There are different sets of rules for different e-mail service providers. Hotmail follows a different set of rules as well. Therefore, it is not easy to pinpoint exactly which rule on the Hotmail service provider is being violated.
To find out the host name for Hotmail, you have to make sure of two things. Firstly, there must be a reverse DNS record for the outbound e-mail server of the user and secondly, the hostname which has been announced by the SMTP server of the user does not match the host name in the reverse DNS record when they connect.
The user could, however, attempt to manually change the properties of his or her virtual SMTP server. Once he or she has changed the properties, they will match. Most people are tight-lipped about their domain names.
To find out the host name for Hotmail, you have to make sure of two things. Firstly, there must be a reverse DNS record for the outbound e-mail server of the user and secondly, the hostname which has been announced by the SMTP server of the user does not match the host name in the reverse DNS record when they connect.
The user could, however, attempt to manually change the properties of his or her virtual SMTP server. Once he or she has changed the properties, they will match. Most people are tight-lipped about their domain names.