Tried and tested solution for RMT shout/yell/tell spam
Before starting Final Fantasy 14, I had been playing Final Fantasy 11 since it was released for the Playstation 2 almost 10 years ago. In 11, there is a chat filter (can be turned on and off) that is constantly updated. The filter is called "Shout messages deemed as spam" and "tell messages deemed as spam". These filters were and still are designed to block anything that looks like a messege from an RMT. For years they have worked almost flawlessly. In 11, I get maybe....one RMT tell a week at most with the spam filter turned on. I have also not heard of any non-RMT messages being blocked with this tool. This is clearly an effective filter that has been been built and updated for the past 5 something years.
Why not just copy and paste this filter into 14? It would stop about 99% of the RMT spam cold.
Or maybe there is some technical hoo-haa that I don't understand which makes it impossible to do this. Just a suggestion.