Very strange the the other dedicated email addresses have never had spam in all the years I have used them!
......Daz email for example has never had this problem.....and it is from the same domain email. I have 18 email addresses, and the only ones that have spam are the ones I use in public, and my private render address.  
Just a coincidence?????:))))) I am through trying to argue with you. The fact is, Render has no plans to do anything about this.