A message-hold decision maker system used with an electronic mail processing system that processes electronic messages for a protected computer network improves the electronic mail processing system's performance by increasing the throughput performance of the system. The improvements are achieved by providing an electronic mail processing gateway with additional logic that makes fast and intelligent decisions on whether to hold, block, allow, or sandbox electronic messages in view of potential threats such as viruses or URL-based threats. A message hold decision maker uses current and stored information from a plurality of specialized classification engines to quickly make the decisions. In some examples, the message hold decision maker will instruct an email gateway to hold an electronic mail message while the classification engines perform further analysis.