I have a customer running Microsoft Exchange 2003 behind a Cisco PIX 501 Firewall. This customer has been getting hit heavily with spam and relay attempts thus loading up the SMTP queue. I am looking into installing some sort of gateway between the firewall and the Exchange server that will filter spam and perform DNS Blacklist lookups then forward good email to the exchange server. I am having a difficult time finding a devise to do this that is not a full fledged firewall and that does DNS blacklist lookups. This customer only has 10 users so i do not need a $4K solution, looking for something between $300 and $700ish. Any suggestions would be great!