Problems on delay with mail replication to server

We have been receiving Notes mail routing delays on an eventful mail server. Pending mail for WAN while connected locations are queued. We have looked into the connectivity of the Notes log server network, for example the trace route, packet sniffing and ping. We still couldn’t find a reason for the delays. Could you inform us how to get a better diagnosis, and also the main cause of this problems we are having?
