The host at this IP address is running a malware botnet controller which is being used to control infected computers (bots) around the globe using a trojan horse.
AZORult botnet controller located at 104.21.20.176 on port 80 (using HTTP POST):
hXXp://e4v5sa.xyz/PL341/index.php
$ dig +short e4v5sa.xyz
104.21.20.176