All Exchange admins are familiar with the SMTP banner. It is the response received by a remote server after it connects to the receive connector of an Exchange 2010 Hub or Edge server. If the SMTP banner is not set on a receive connector, the default response will have the fqdn of the server, along with the information that the server in use is a Microsoft one.
Below is the default response from my telnet client. As the internal information becomes visible to outside servers, exchange admins tend to change it.
I have seen companies using the “Specify the fqdn this connector will provide in response to EHLO” option in the receive connector as a means to set the banner. It is NOT the right way to do it.
--> The rest is on the blog : http://www.howexchangeworks.com/2011/06/setting-smtp-banner-in-exchange-2010.html