[CentOS] SYD flood dropped on Sendmail (centos 4.x)

My guys,

My firewall seems to block an attack my Centos / Sendmail boxes on port 110. These servers require a reboot after each attack. My firewall says it's blocked? Do I need to patch something on sendmail? Or is my firewall not doing its job (Sonicwall)? This is not the first time this has happened.

11/20/2008 02:53:04.864 - SYN flood attack dropped - 75.2.205.141, 48102 - 10.80.80.210, 110

11/20/2008 03:08:04.864 - SYN flood attack dropped - 75.2.205.141, 64955, greatcooks.biz - 10.80.80.220, 110

11/20/2008 03:23:08.864 - SYN flood attack dropped - 75.2.205.141, 43068, greatcooks.biz - 10.80.80.210, 110

Any input would be much appreciated.

Thanks.