diff --git a/lib/pleroma/web/activity_pub/mrf/anti_hellthread_policy.ex b/lib/pleroma/web/activity_pub/mrf/anti_hellthread_policy.ex
new file mode 100644
index 000000000..4b52fb4fd
--- /dev/null
+++ b/lib/pleroma/web/activity_pub/mrf/anti_hellthread_policy.ex
@@ -0,0 +1,90 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2022 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.ActivityPub.MRF.AntiHellthreadPolicy do
+  @moduledoc "Notify local users upon remote block."
+  @behaviour Pleroma.Web.ActivityPub.MRF.Policy
+
+  alias Pleroma.User
+  alias Pleroma.Web.CommonAPI
+
+  defp is_block_or_unblock(%{"type" => "Block", "object" => object}),
+    do: {true, "blocked", object}
+
+  defp is_block_or_unblock(%{
+         "type" => "Undo",
+         "object" => %{"type" => "Block", "object" => object}
+       }),
+       do: {true, "unblocked", object}
+
+  defp is_block_or_unblock(_), do: {false, nil, nil}
+
+  defp is_remote_or_displaying_local?(%User{local: false}), do: true
+
+  defp is_remote_or_displaying_local?(_),
+    do: Pleroma.Config.get([:mrf_anti_hellthread_policy, :display_local])
+
+  @impl true
+  def filter(message) do
+    with {true, action, object} <- is_block_or_unblock(message),
+         %User{} = actor <- User.get_cached_by_ap_id(message["actor"]),
+         %User{} = recipient <- User.get_cached_by_ap_id(object),
+         true <- recipient.local,
+         true <- is_remote_or_displaying_local?(actor),
+         false <- User.blocks_user?(recipient, actor) do
+      bot_user = Pleroma.Config.get([:mrf_anti_hellthread_policy, :user])
+
+      _reply =
+        CommonAPI.post(User.get_by_nickname(bot_user), %{
+          status:
+            "@" <> recipient.nickname <> " you have been " <> action <> " by @" <> actor.nickname,
+          visibility: "direct"
+        })
+    end
+
+    {:ok, message}
+  end
+
+  @impl true
+  @spec config_description :: %{
+          children: [
+            %{
+              description: <<_::200, _::_*24>>,
+              key: :display_local | :user,
+              suggestions: [...],
+              type: :boolean | :string
+            },
+            ...
+          ],
+          description: <<_::296>>,
+          key: :mrf_anti_hellthread_policy,
+          label: <<_::208>>,
+          related_policy: <<_::384>>
+        }
+  def config_description do
+    %{
+      key: :mrf_anti_hellthread_policy,
+      related_policy: "Pleroma.Web.ActivityPub.MRF.AntiHellthreadPolicy",
+      label: "MRF Anti Hellthread Policy",
+      description: "Notify local users upon remote block.",
+      children: [
+        %{
+          key: :user,
+          type: :string,
+          description: "The user who will notify of the block",
+          suggestions: ["blockbot"]
+        },
+        %{
+          key: :display_local,
+          type: :boolean,
+          description: "Display blocks from local users as well?",
+          suggestions: [false]
+        }
+      ]
+    }
+  end
+
+  @impl true
+  def describe, do: {:ok, %{}}
+end