We are considering using free RBL services for the first time in Exchange 2007. We have an Edge server which catches most spam however some still slip through most likely because they are from newly infected bot machines. We are considering using some or all of the following free RBL providers:
If one or more RBL providers are added to Exchange when does it block the e-mail? If only one reports it is on a black list? If a majority indicate it is? What if we use only one, e.g. spamhaus, and spamhaus is "down" when it goes to check. Will the any and all incoming e-mail be queued up since it cannot be checked? Or will it all come through unchecked? It will be appreciated if someone can help me understand how this will work.