diff --git a/changelog.d/optimistic-inbox.change b/changelog.d/optimistic-inbox.change
new file mode 100644
index 000000000..2cf1ce92c
--- /dev/null
+++ b/changelog.d/optimistic-inbox.change
@@ -0,0 +1 @@
+Optimistic Inbox reduces the processing overhead of incoming activities without instantly verifiable signatures.
diff --git a/lib/pleroma/user.ex b/lib/pleroma/user.ex
index ce125d608..0706f5607 100644
--- a/lib/pleroma/user.ex
+++ b/lib/pleroma/user.ex
@@ -2136,7 +2136,7 @@ def public_key(%{public_key: public_key_pem}) when is_binary(public_key_pem) do
   def public_key(_), do: {:error, "key not found"}
 
   def get_public_key_for_ap_id(ap_id) do
-    with {:ok, %User{} = user} <- get_or_fetch_by_ap_id(ap_id),
+    with %User{} = user <- get_cached_by_ap_id(ap_id),
          {:ok, public_key} <- public_key(user) do
       {:ok, public_key}
     else
diff --git a/lib/pleroma/web/activity_pub/activity_pub_controller.ex b/lib/pleroma/web/activity_pub/activity_pub_controller.ex
index 1357c379c..3b2193ca3 100644
--- a/lib/pleroma/web/activity_pub/activity_pub_controller.ex
+++ b/lib/pleroma/web/activity_pub/activity_pub_controller.ex
@@ -287,10 +287,9 @@ def inbox(%{assigns: %{valid_signature: true}} = conn, params) do
     json(conn, "ok")
   end
 
-  def inbox(%{assigns: %{valid_signature: false}} = conn, _params) do
-    conn
-    |> put_status(:bad_request)
-    |> json("Invalid HTTP Signature")
+  def inbox(%{assigns: %{valid_signature: false}, req_headers: req_headers} = conn, params) do
+    Federator.incoming_ap_doc(%{req_headers: req_headers, params: params})
+    json(conn, "ok")
   end
 
   # POST /relay/inbox -or- POST /internal/fetch/inbox
diff --git a/lib/pleroma/web/federator.ex b/lib/pleroma/web/federator.ex
index 84b77cda1..8621d984c 100644
--- a/lib/pleroma/web/federator.ex
+++ b/lib/pleroma/web/federator.ex
@@ -35,6 +35,17 @@ def allowed_thread_distance?(distance) do
   end
 
   # Client API
+  def incoming_ap_doc(%{params: params, req_headers: req_headers}) do
+    ReceiverWorker.enqueue(
+      "incoming_ap_doc",
+      %{"req_headers" => req_headers, "params" => params, "timeout" => :timer.seconds(20)},
+      priority: 2
+    )
+  end
+
+  def incoming_ap_doc(%{"type" => "Delete"} = params) do
+    ReceiverWorker.enqueue("incoming_ap_doc", %{"params" => params}, priority: 3)
+  end
 
   def incoming_ap_doc(params) do
     ReceiverWorker.enqueue("incoming_ap_doc", %{"params" => params})
diff --git a/lib/pleroma/workers/receiver_worker.ex b/lib/pleroma/workers/receiver_worker.ex
index cf1bb62b4..1dddd8d2e 100644
--- a/lib/pleroma/workers/receiver_worker.ex
+++ b/lib/pleroma/workers/receiver_worker.ex
@@ -3,24 +3,56 @@
 # SPDX-License-Identifier: AGPL-3.0-only
 
 defmodule Pleroma.Workers.ReceiverWorker do
+  alias Pleroma.Signature
+  alias Pleroma.User
   alias Pleroma.Web.Federator
 
   use Pleroma.Workers.WorkerHelper, queue: "federator_incoming"
 
   @impl Oban.Worker
+
+  def perform(%Job{
+        args: %{"op" => "incoming_ap_doc", "req_headers" => req_headers, "params" => params}
+      }) do
+    # Oban's serialization converts our tuple headers to lists.
+    # Revert it for the signature validation.
+    req_headers = Enum.into(req_headers, [], &List.to_tuple(&1))
+
+    conn_data = %{params: params, req_headers: req_headers}
+
+    with {:ok, %User{} = _actor} <- User.get_or_fetch_by_ap_id(conn_data.params["actor"]),
+         {:ok, _public_key} <- Signature.refetch_public_key(conn_data),
+         {:signature, true} <- {:signature, HTTPSignatures.validate_conn(conn_data)},
+         {:ok, res} <- Federator.perform(:incoming_ap_doc, params) do
+      {:ok, res}
+    else
+      e -> process_errors(e)
+    end
+  end
+
   def perform(%Job{args: %{"op" => "incoming_ap_doc", "params" => params}}) do
     with {:ok, res} <- Federator.perform(:incoming_ap_doc, params) do
       {:ok, res}
     else
+      e -> process_errors(e)
+    end
+  end
+
+  @impl Oban.Worker
+  def timeout(%_{args: %{"timeout" => timeout}}), do: timeout
+
+  def timeout(_job), do: :timer.seconds(5)
+
+  defp process_errors(errors) do
+    case errors do
       {:error, :origin_containment_failed} -> {:cancel, :origin_containment_failed}
       {:error, :already_present} -> {:cancel, :already_present}
       {:error, {:validate_object, reason}} -> {:cancel, reason}
       {:error, {:error, {:validate, reason}}} -> {:cancel, reason}
       {:error, {:reject, reason}} -> {:cancel, reason}
+      {:signature, false} -> {:cancel, :invalid_signature}
+      {:error, {:error, reason = "Object has been deleted"}} -> {:cancel, reason}
       e -> e
     end
   end
-
-  @impl Oban.Worker
-  def timeout(_job), do: :timer.seconds(5)
 end
diff --git a/test/pleroma/signature_test.exs b/test/pleroma/signature_test.exs
index b849cbee7..f5a915fa8 100644
--- a/test/pleroma/signature_test.exs
+++ b/test/pleroma/signature_test.exs
@@ -43,10 +43,7 @@ test "it returns key" do
     end
 
     test "it returns error when not found user" do
-      assert capture_log(fn ->
-               assert Signature.fetch_public_key(make_fake_conn("https://test-ap-id")) ==
-                        {:error, :error}
-             end) =~ "[error] Could not decode user"
+      assert Signature.fetch_public_key(make_fake_conn("https://test-ap-id")) == {:error, :error}
     end
 
     test "it returns error if public key is nil" do
diff --git a/test/pleroma/user_test.exs b/test/pleroma/user_test.exs
index b9df527a0..77ca9198b 100644
--- a/test/pleroma/user_test.exs
+++ b/test/pleroma/user_test.exs
@@ -1951,8 +1951,8 @@ test "unsuggests a user" do
     end
   end
 
-  test "get_public_key_for_ap_id fetches a user that's not in the db" do
-    assert {:ok, _key} = User.get_public_key_for_ap_id("http://mastodon.example.org/users/admin")
+  test "get_public_key_for_ap_id returns correctly for user that's not in the db" do
+    assert :error = User.get_public_key_for_ap_id("http://mastodon.example.org/users/admin")
   end
 
   describe "per-user rich-text filtering" do