A system and method for providing dynamic screening of transient messages in a distributed computing environment is disclosed. An incoming message is intercepted at a network domain boundary. The incoming message includes a header having a plurality of address fields, each storing contents. A set of blocking rules is maintained. Each blocking rule defines readily-discoverable characteristics indicative of messages infected with at least one of a computer virus, malware and bad content. The contents of each address field are identified and checked against the blocking rules to screen infected messages and identify clean messages. Each such clean message is staged into an intermediate message queue pending further processing.