Buffer overflow in Internet Mail Connector (IMC) for Microsoft Exchange Server 5.5 allows remote attackers to execute arbitrary code via an EHLO request from a system with a long name as obtained through a reverse DNS lookup, which triggers the overflow in IMC's hello response.
https://docs.microsoft.com/en-us/security-updates/securitybulletins/2002/ms02-037
http://www.securityfocus.com/bid/5306
http://support.microsoft.com/default.aspx?scid=kb%3B%5BLN%5D%3BQ326322