I am sorry to hear that my previous attempt at stopping PM spam didn't have as much of an effect as I liked and some of you received a spam PM in your inbox. I apologise for this inconvenience. They have now been banned and I have spoken with the mods and community team and have come up with a solution.
So with this in mind, I am going to be doing some changes this afternoon to ensure that this never happens again (or at least curbs any future attemps). This is basically my other plan if the first one was not effective.
I will not be divulging too much information about the work being done as a potential spammer could read what I have done and get around it. I have been given the green light by the Community Help team as well as the Moderators here and they agree that the changes should put a stop to this without hindering genuine users who require help and need to use the PM system. I will be implementing restrictions right now with IMMEDIATE EFFECT.
Please note that none of you should be affected by any of my changes. The things I am going to be putting in place will help us identify a spammer before they can do anything and we can deal with them appropriately.