Movinon,
I don't know that I have a black belt, but surely some experience with divorcing an nh who was hiding assets and income. By the time we got to mediation, I had at least enough documentation to stand 2 feet high (I am not exaggerating). I did receive e-mails similar to the one you received over the course of the 18 months it took the divorce to occur, but as Stormy suggested, I passed them off to my attorney to handle.
I will admit to using some rather unethical methods in order to find out information (my attorney did not know how I got the info), but it did confirm that he and his father were collaborating to hide income, so I knew there was a reason to keep fighting. My attorney hired a forensic accountant to do all the investigating at my xh's firm, review tax records, etc. This may be something you would wish to explore. It obviously adds to the costs, so you have to decide if it's worth it.
I know I have heard you mention that your stbxh is afraid of being exposed. This was true of mine as well and I really used that to my advantage when we ended up in mediation. I will say that I carefully poured over all the documentation prior to the mediation session and was able to point out inconsistencies to my attorney and the forensic accountant that they missed. My attorney was threatening to depose him regarding all his finances as a result and he clearly did not want to have to testify under oath and finally caved into my financial demands.
Fortunately, I didn't have to worry about the kids with him, so that was never an issue. I'm not sure how you can handle that except with the psych eval. Mum would know more about that than I.
Hope that helps a little.
Brigid