Outbound Messages are rejected by ISP

I am using Symantec anitvirus 10.1.6.6000 scan engine 101.3.0.93 version 3/23/2011 rev. 2. I am running ThunderBird on XP.

There is no way to disable outbound scans in my Symantec window. I have to send my messages twice sometimes three and

four times before Earthlink will accept them. I get the failure message even before the scan window has finished. All of this was

working fine up until Oct. 2010. Is there a solution?