How does Exchange 2000 Server decide which bridgehead server to use for communications within a routing group?
Each time an Exchange server initiates a new SMTP session to a host in the same routing group, the routing engine must choose a remote bridgehead. When only one bridgehead server exists in the routing group, the selection process is simple. When multiple bridgeheads exist, the routing engine first sorts the servers by their link state table status; servers that appear to be down go to the end of the list. The routing engine then randomly chooses a server from the list of operational servers and uses that server for the entire SMTP session. Depending on how many messages need to be transferred and the arrival rate of those messages, the session might be open for some time or might terminate after only a few messages. Exchange repeats the process every time a new session is established.