Well, there should be an option in serveroptions.txt which allows you to turn on/off PMs, like this:
allowpms = 0
(0 for false, 1 for true)
Murasamune needs PMs to be off to truely integrate the messaging system, and to make things more like the time setting...
I mean, who could instantly send a message to someone in far older times? Not the common person...or anyone for that matter
.