Integer overflow in eXtremail 2.1.1 and earlier allows remote attackers to cause a denial of service, and possibly execute arbitrary code, via a long USER command containing "%s" sequences to the pop3 port (110/tcp), which are expanded to "%%s" before being used in the memmove function, possibly due to an incomplete fix for CVE-2001-1078.
https://www.exploit-db.com/exploits/4532
http://www.securityfocus.com/bid/26074
http://www.securityfocus.com/archive/1/482293