Currently, a Domino server will log that it has delivered NRPC based mail to a database or transferred mail to another server including who the message is for and who sent it. However, it does not log the source of the message. There is no record to show if the message originated from a Notes client, from an agent or process on the same server or was transferred from another server.
With SMTP mail, on the other hand, the source of the message is logged as well as where the message was delivered or transferred to. It also logs who sent the message and who it was from. This makes it very easy to trace backwards to where a message originally came from.