mail.local in Sendmail 8.10.x does not properly identify the .\n string which identifies the end of message text, which allows a remote attacker to cause a denial of service or corrupt mailboxes via a message line that is 2047 characters long and ends in .\n.
http://www.securityfocus.com/templates/archive.pike?list=1&msg=2694.000424%40SECURITY.NNOV.RU