The POP3 mail client in Mozilla 1.0 and earlier, and Netscape Communicator 4.7 and earlier, allows remote attackers to cause a denial of service (no new mail) via a mail message containing a dot (.) at a newline, which is interpreted as the end of the message.
http://www.securityfocus.com/archive/1/276946
http://www.mandrakesoft.com/security/advisories?name=MDKSA-2002:074
http://www.iss.net/security_center/static/9343.php
http://online.securityfocus.com/archive/1/276628
http://mozilla.org/releases/mozilla1.0.1/security-fixes-1.0.1.html