The SMTP banner is the message which the remote mail servers receive when establishing an SMTP connection to a receive connector on Exchange Server 2007. By default the initial message has the following format:
220 ExchangeInternalName Microsoft ESMTP MAIL service ready at Date-Hour-Time
Disclosing the internal Active Directory name and the type of the mail server to the outside world is definitely not a good idea, from security point of view. It is recommended to change the default SMTP response. Note that the response has to be RFC 2821 compliant and start with code 220, followed by space.
In the following Step-by-Step Screencast, we will demonstrate how to configure the SMTP banner in Exchange Server 2007 SP1. You can get the list of Exchange Management Shell commands used in the demo from here