After testing in nine Sbs2k3 (Small Business Server 2003) boxes managed by me, I added the IP address of the POP3 servers to the hosts file, and it completely cleared the event and all other related to POP3 connector. This is not the best solution because you have to verify if the ISP changes the IP, but this solved the issue.
My issue was resolved after I turn off the EDNS0 feature in Windows Server 2003. See ME832223
for information on this problem.
Several newsgroup posts suggest that this is related to the size of the MTU on the router used to connect to the Internet. See "EventID 1035 from source POP3 Connector" for more details on this issue.
We see this as a general error when the pop3 connector in Exchange 2003 for SBS is unable to download the message for some reason (pop3 server down). You must look for other errors that follow for the specific problem.