A SYN attack refers to an intruder proliferating SYN (synchronizing character) messages in a malicious attempt to deny users access to a server by generating an overwhelming amount of half-open Transmission Control Protocol (TCP) port connections.
You can prevent Internet "mail bombings" ¾ unwanted incoming mass electronic messages ¾ by judicious use of IP address settings and permissions. However, protecting your Web site against SYN attacks is not so simple.