See KB281224 for full details, but in short:
This may be an issue if you do not want the version of the SMTP service that
is running on your server to be displayed. To remove the version information
from the Windows 2000 SMTP banner, follow these steps:
1.. Using a metabase editing tool such as MetaEdit, locate the following
Lm\Smtpsvc\virtual server number
2.. Click Edit, click New, and then click String.
3.. Verify that the entry in the ID box is Other, and then type 36907
(decimal) on the right side of the ID box.
4.. In the Value box, type the banner that you want to be displayed.
5.. Stop, and then restart the SMTP virtual server or the SMTP service.
To confirm that the banner has been changed, telnet to port 25 of the
virtual server (the default setting). The "ESMTP MAIL Service, Version:
5.0.2195.1600" banner should no longer be displayed.
> How can I modify the banner info that EX 2000 provides on the SMTP port?
> Currently it gives the server name, Microsoft ESMTP MAIL Service Version.
> I'd like to have it provide no version info and a different server name
> (currently shows the actual internal name instead of mail.domain.com)