Mojang recently introduced a blacklisting mechanism which allowed Mojang to block servers that violate the Minecraft End User License Agreement
And then shortly after in 1.9.3 Pre-Release 3 it went missing again
Only to be brought back later inside a modified Netty dependency
See: this decompiled version of their netty bootstrap.java
This repository is being updated every five minutes, and it attempts to utilize the dictionary in support/dictionary to determine which server(s) have been blocked by Mojang.
IF YOU HAPPEN TO RUN, OR KNOW PEOPLE THAT MANAGE TOPSITES PLEASE ASK THEM VERY POLITELY TO SHARE THEIR HOSTNAMES WITH ME SO I CAN ADD THEM TO OUR DICTIONARY!