First off thanks for using NVN!
Secondly, I'm not deleting any messages BUT I think that this is a side effect of my setting a limit on PM's to prevent spam. We had a person spam a whole heap of members before Xmas so I tried to put in place measures to prevent this.
I'll go back and check the settings, apologies.
But just to be clear, I'm not deleting any, it's probably the database somehow doing it automatically...