In game advertisements, we all get them when we walk near the famous bots. The places from these bots are already send to customer support but the answer we get back is just to use blacklist. Wrong! Blacklisting will not help against in game messages and once discovered by a bot we will get messages like... forever... Quoting one:
We invite you to buy cheap gold coins from 8 cents per 1mil on [bad website]. No any scam, no need to enter your account information. Pay easy via PayPal. Buy now and save money!
The problem is that PWE also knows the abusing, which happens in all the games and all servers from PWE. In other words: we've got a verified seller. Now a suggestion: since blocking isn't impossible the procedure to send in-game mail need to change: (in all games published by PWE): players should be able to send in game mail ONLY to other players via the friend list. In addition: the mail would only arrive if the sender is in the friend list of the receiver, PWE could also take legal actions to the abusers but that costs more time than a little change in the sourcecode.