The remote host is subject to the 'smad' attack(sendmail accept dos). Description : Smad prevents sendmail from accepting legitimate connections. A cracker may use this flaw to prevent you from receiving any email, thus lowering the interest of being connected to internet. This attack is specific to some versions of the Linux kernel. There are various security bugs in the implementation of this service which can be used by an intruder to gain a root account rather easily. Reference : http://online.securityfocus.com/archive/1/11073

upgrade your Linux kernel to a newer version or filter incoming traffic to this port.