I wrote about changing it in the past for Exchange 2003 but today I had to revisit an Exchange 2000 server so I figured I'd write down the steps I took to get the job done.
First, I downloaded Metaedit 2.2 from Microsoft's website:
http://download.microsoft.com/download/iis50/utility/5.0/nt45/en-us/mtaedt22.exe
It will try to overwrite common system files that are newer than what is packaged with MetaEdit. Alway keep the most recent copy of the DLLs, so answer 'Yes' when it complains.
Launch MetaEdit and drill down to "LM\SmtpSvc\[your virtual SMTP server]" where [your virtual SMTP server] is typically '1' on standard setups. Inside there, insert a 'String' with an Id of 'Other' and a number of 36907. In the data field, enter in what you want the banner to say. I typically set it to:
"** Unauthorized use and unsolicited commercial e-mail prohibited (NO UCE) **"
Before the edit, connecting directly to the SMTP port looked like this:
220 mail.clownballoons.com Microsoft ESMTP MAIL Service, Version: 5.0.2195.xxxx ready at Thu, 16 Mar 2006 11:24:06 -0500
After the edit, and restarting the SMTP service, it should look like:
220 mail.clownballons.com ** Unauthorized use and unsolicited commercial e-mail prohibited (NO UCE) ** Thu, 16 Mar 2006 11:24:06 -0500
Why is it sometimes a good idea to do this? There are bots out there looking for Exchange servers with specific version numbers and by default, the banner gives that information away. It won't stop a smart hacker, but it will fool/obscure the script kiddies.