1. Use MetaEdit and locate the following file:
   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 on the right side of the ID box
4. In the Data box, type the banner that you want to be displayed...

 SMTPConnectionString - 36907 MAILSRVR
 POP3ConnectionString - 41661 POP3SRVR
 POP3DisconnectionString - 41662 POP3SRVR Goodbye
 IMAP4ConnectionString - 49884 IMAP4SRVR
 IMAP4DisconnectionString - 49885 IMAP4SRVR Goodbye


How to Modify the SMTP Banner
http://support.microsoft.com/?kbid=281224

How to modify the POP or IMAP banner
http://support.microsoft.com/?kbid=303513

IIS MetaEdit 2.2 Utility
http://support.microsoft.com/?kbid=232068