Disabling or Limiting tells

[Kanash]

Put yourself on "Busy" mode. That blocks any incoming /tell. You cant recieve party invites either, but are still able to join dungeons via DF.
Sadly, there is no option to limit tells to Friends only.

Or you can just add the RMT to your blacklist. That's what everyone else does

And with a full blacklist, that is no longer an option.