It is the sender who is being rejected, NOT the recipient. Your server IS NOT accepting messages from a known problem IP. The message is coming from an IP that is listed on xbl.spamhaus.org
Search here
http://www.spamhaus.org/xbl/index.lassoYou see it is listed on
CBL - Composite Blocking List
The CBL takes its source data from very large spamtraps, and only lists IPs exhibiting characteristics which are specific to open proxies of various sorts (HTTP, socks, AnalogX, wingate etc) which have been abused to send spam, worms/viruses that do their own direct mail transmission, or some types of trojan-horse or "stealth" spamware, without doing open proxy tests of any kind.
See
http://cbl.abuseat.org/lookup.cgi?ip=129.33.49.251&.submit=LookupYou can request it be removed BUT you better find out why it is listed, as it will only get listed again later (for longer & possibly permanently).
Have you got an open relay there or something ?
You might want to remove the xbl.spamhaus.org list from the RBLList property temporarily
Regs
Ray