diff --git a/changelog.d/19955.feature b/changelog.d/19955.feature
new file mode 100644
index 00000000000..534f4943ec3
--- /dev/null
+++ b/changelog.d/19955.feature
@@ -0,0 +1 @@
+Push relevant users if there's a knock on a room (MSC4506).
diff --git a/rust/benches/evaluator.rs b/rust/benches/evaluator.rs
index 96169fd45d9..44059327503 100644
--- a/rust/benches/evaluator.rs
+++ b/rust/benches/evaluator.rs
@@ -57,6 +57,7 @@ fn bench_match_exact(b: &mut Bencher) {
         Some(0),
         Default::default(),
         Default::default(),
+        Default::default(),
         true,
         vec![],
         false,
@@ -72,10 +73,15 @@ fn bench_match_exact(b: &mut Bencher) {
         },
     ));
 
-    let matched = eval.match_condition(&condition, None, None, None).unwrap();
+    let matched = eval
+        .match_condition(&condition, None, None, None, None)
+        .unwrap();
     assert!(matched, "Didn't match");
 
-    b.iter(|| eval.match_condition(&condition, None, None, None).unwrap());
+    b.iter(|| {
+        eval.match_condition(&condition, None, None, None, None)
+            .unwrap()
+    });
 }
 
 #[bench]
@@ -104,6 +110,7 @@ fn bench_match_word(b: &mut Bencher) {
         Some(0),
         Default::default(),
         Default::default(),
+        Default::default(),
         true,
         vec![],
         false,
@@ -119,10 +126,15 @@ fn bench_match_word(b: &mut Bencher) {
         },
     ));
 
-    let matched = eval.match_condition(&condition, None, None, None).unwrap();
+    let matched = eval
+        .match_condition(&condition, None, None, None, None)
+        .unwrap();
     assert!(matched, "Didn't match");
 
-    b.iter(|| eval.match_condition(&condition, None, None, None).unwrap());
+    b.iter(|| {
+        eval.match_condition(&condition, None, None, None, None)
+            .unwrap()
+    });
 }
 
 #[bench]
@@ -151,6 +163,7 @@ fn bench_match_word_miss(b: &mut Bencher) {
         Some(0),
         Default::default(),
         Default::default(),
+        Default::default(),
         true,
         vec![],
         false,
@@ -166,10 +179,15 @@ fn bench_match_word_miss(b: &mut Bencher) {
         },
     ));
 
-    let matched = eval.match_condition(&condition, None, None, None).unwrap();
+    let matched = eval
+        .match_condition(&condition, None, None, None, None)
+        .unwrap();
     assert!(!matched, "Didn't match");
 
-    b.iter(|| eval.match_condition(&condition, None, None, None).unwrap());
+    b.iter(|| {
+        eval.match_condition(&condition, None, None, None, None)
+            .unwrap()
+    });
 }
 
 #[bench]
@@ -198,6 +216,7 @@ fn bench_eval_message(b: &mut Bencher) {
         Some(0),
         Default::default(),
         Default::default(),
+        Default::default(),
         true,
         vec![],
         false,
@@ -215,7 +234,8 @@ fn bench_eval_message(b: &mut Bencher) {
         false,
         false,
         false,
+        false,
     );
 
-    b.iter(|| eval.run(&rules, Some("bob"), Some("person"), None));
+    b.iter(|| eval.run(&rules, Some("bob"), Some("person"), None, None));
 }
diff --git a/rust/src/push/base_rules.rs b/rust/src/push/base_rules.rs
index 47d5289006b..3db3a287d9e 100644
--- a/rust/src/push/base_rules.rs
+++ b/rust/src/push/base_rules.rs
@@ -117,6 +117,30 @@ pub const BASE_APPEND_OVERRIDE_RULES: &[PushRule] = &[
         default: true,
         default_enabled: true,
     },
+    // MSC4506: notify the members of a room who are able to act on a knock
+    // (i.e. those with a power level sufficient to invite the knocker). Must
+    // come before `.m.rule.member_event`, which suppresses all other member
+    // events.
+    PushRule {
+        rule_id: Cow::Borrowed("global/override/.org.matrix.msc4506.rule.knock"),
+        priority_class: 5,
+        conditions: Cow::Borrowed(&[
+            Condition::Known(KnownCondition::EventMatch(EventMatchCondition {
+                key: Cow::Borrowed("type"),
+                pattern: Cow::Borrowed("m.room.member"),
+            })),
+            Condition::Known(KnownCondition::EventMatch(EventMatchCondition {
+                key: Cow::Borrowed("content.membership"),
+                pattern: Cow::Borrowed("knock"),
+            })),
+            Condition::Known(KnownCondition::RecipientPermission {
+                key: Cow::Borrowed("invite"),
+            }),
+        ]),
+        actions: Cow::Borrowed(&[Action::Notify, HIGHLIGHT_FALSE_ACTION, SOUND_ACTION]),
+        default: true,
+        default_enabled: true,
+    },
     PushRule {
         rule_id: Cow::Borrowed("global/override/.m.rule.member_event"),
         priority_class: 5,
diff --git a/rust/src/push/evaluator.rs b/rust/src/push/evaluator.rs
index 1cbca4c6355..b47033b8015 100644
--- a/rust/src/push/evaluator.rs
+++ b/rust/src/push/evaluator.rs
@@ -92,6 +92,12 @@ pub struct PushRuleEvaluator {
     /// outlier.
     sender_power_level: Option<i64>,
 
+    /// MSC4506: the power level required to perform each of the room's
+    /// power-levels actions (e.g. "invite", "kick"), for the
+    /// `recipient_permission` condition. Includes the spec defaults for
+    /// actions absent from the `m.room.power_levels` content.
+    action_power_levels: BTreeMap<String, i64>,
+
     /// The related events, indexed by relation type. Flattened in the same manner as
     /// `flattened_keys`.
     related_events_flattened: BTreeMap<String, BTreeMap<String, JsonValue>>,
@@ -124,6 +130,7 @@ impl PushRuleEvaluator {
         room_member_count,
         sender_power_level,
         notification_power_levels,
+        action_power_levels,
         related_events_flattened,
         related_event_match_enabled,
         room_version_feature_flags,
@@ -137,6 +144,7 @@ impl PushRuleEvaluator {
         room_member_count: u64,
         sender_power_level: Option<i64>,
         notification_power_levels: BTreeMap<String, i64>,
+        action_power_levels: BTreeMap<String, i64>,
         related_events_flattened: BTreeMap<String, BTreeMap<String, JsonValue>>,
         related_event_match_enabled: bool,
         room_version_feature_flags: Vec<String>,
@@ -156,6 +164,7 @@ impl PushRuleEvaluator {
             room_member_count,
             notification_power_levels,
             sender_power_level,
+            action_power_levels,
             related_events_flattened,
             related_event_match_enabled,
             room_version_feature_flags,
@@ -179,13 +188,17 @@ impl PushRuleEvaluator {
     /// - `None` if the event is not in a thread, or if MSC4306 is disabled.
     /// - `Some(true)` if the event is in a thread and the user has a subscription for that thread
     /// - `Some(false)` if the event is in a thread and the user does NOT have a subscription for that thread
-    #[pyo3(signature = (push_rules, user_id=None, display_name=None, msc4306_thread_subscription_state=None))]
+    ///
+    /// recipient_power_level: the power level of the user the rules are being
+    /// evaluated for, used by the MSC4506 `recipient_permission` condition.
+    #[pyo3(signature = (push_rules, user_id=None, display_name=None, msc4306_thread_subscription_state=None, recipient_power_level=None))]
     pub fn run(
         &self,
         push_rules: &FilteredPushRules,
         user_id: Option<&str>,
         display_name: Option<&str>,
         msc4306_thread_subscription_state: Option<bool>,
+        recipient_power_level: Option<i64>,
     ) -> Vec<Action> {
         'outer: for (push_rule, enabled) in push_rules.iter() {
             if !enabled {
@@ -222,6 +235,7 @@ impl PushRuleEvaluator {
                     user_id,
                     display_name,
                     msc4306_thread_subscription_state,
+                    recipient_power_level,
                 ) {
                     Ok(true) => {}
                     Ok(false) => continue 'outer,
@@ -255,19 +269,21 @@ impl PushRuleEvaluator {
     }
 
     /// Check if the given condition matches.
-    #[pyo3(signature = (condition, user_id=None, display_name=None, msc4306_thread_subscription_state=None))]
+    #[pyo3(signature = (condition, user_id=None, display_name=None, msc4306_thread_subscription_state=None, recipient_power_level=None))]
     fn matches(
         &self,
         condition: Condition,
         user_id: Option<&str>,
         display_name: Option<&str>,
         msc4306_thread_subscription_state: Option<bool>,
+        recipient_power_level: Option<i64>,
     ) -> bool {
         match self.match_condition(
             &condition,
             user_id,
             display_name,
             msc4306_thread_subscription_state,
+            recipient_power_level,
         ) {
             Ok(true) => true,
             Ok(false) => false,
@@ -287,6 +303,7 @@ impl PushRuleEvaluator {
         user_id: Option<&str>,
         display_name: Option<&str>,
         msc4306_thread_subscription_state: Option<bool>,
+        recipient_power_level: Option<i64>,
     ) -> Result<bool, Error> {
         let known_condition = match condition {
             Condition::Known(known) => known,
@@ -409,6 +426,18 @@ impl PushRuleEvaluator {
                     false
                 }
             }
+            KnownCondition::RecipientPermission { key } => {
+                if let Some(recipient_power_level) = recipient_power_level {
+                    if let Some(required_level) = self.action_power_levels.get(key.as_ref()) {
+                        recipient_power_level >= *required_level
+                    } else {
+                        // Unknown action keys never match.
+                        false
+                    }
+                } else {
+                    false
+                }
+            }
             KnownCondition::RoomVersionSupports { feature } => {
                 if !self.msc3931_enabled {
                     false
@@ -564,6 +593,7 @@ fn push_rule_evaluator() {
         Some(0),
         BTreeMap::new(),
         BTreeMap::new(),
+        BTreeMap::new(),
         true,
         vec![],
         true,
@@ -572,10 +602,68 @@ fn push_rule_evaluator() {
     )
     .unwrap();
 
-    let result = evaluator.run(&FilteredPushRules::default(), None, Some("bob"), None);
+    let result = evaluator.run(&FilteredPushRules::default(), None, Some("bob"), None, None);
     assert_eq!(result.len(), 3);
 }
 
+#[test]
+fn test_recipient_permission_condition() {
+    let mut action_power_levels = BTreeMap::new();
+    action_power_levels.insert("invite".to_string(), 50);
+
+    let evaluator = PushRuleEvaluator::py_new(
+        BTreeMap::new(),
+        false,
+        10,
+        Some(0),
+        BTreeMap::new(),
+        action_power_levels,
+        BTreeMap::new(),
+        true,
+        vec![],
+        true,
+        false,
+        false,
+    )
+    .unwrap();
+
+    let condition = Condition::Known(KnownCondition::RecipientPermission {
+        key: Cow::Borrowed("invite"),
+    });
+
+    // A recipient at or above the required level matches.
+    assert!(evaluator
+        .match_condition(&condition, Some("@bob:example.org"), None, None, Some(50))
+        .unwrap());
+    assert!(evaluator
+        .match_condition(&condition, Some("@bob:example.org"), None, None, Some(100))
+        .unwrap());
+
+    // A recipient below the required level does not match.
+    assert!(!evaluator
+        .match_condition(&condition, Some("@bob:example.org"), None, None, Some(0))
+        .unwrap());
+
+    // No recipient power level provided: never matches.
+    assert!(!evaluator
+        .match_condition(&condition, Some("@bob:example.org"), None, None, None)
+        .unwrap());
+
+    // An action key we don't have a level for never matches.
+    let unknown_key = Condition::Known(KnownCondition::RecipientPermission {
+        key: Cow::Borrowed("frobnicate"),
+    });
+    assert!(!evaluator
+        .match_condition(
+            &unknown_key,
+            Some("@bob:example.org"),
+            None,
+            None,
+            Some(100)
+        )
+        .unwrap());
+}
+
 #[test]
 fn test_requires_room_version_supports_condition() {
     use std::borrow::Cow;
@@ -595,6 +683,7 @@ fn test_requires_room_version_supports_condition() {
         Some(0),
         BTreeMap::new(),
         BTreeMap::new(),
+        BTreeMap::new(),
         false,
         flags,
         true,
@@ -610,6 +699,7 @@ fn test_requires_room_version_supports_condition() {
         Some("@bob:example.org"),
         None,
         None,
+        None,
     );
     assert_eq!(result.len(), 3);
 
@@ -637,10 +727,12 @@ fn test_requires_room_version_supports_condition() {
             false,
             false,
             false,
+            false,
         ),
         None,
         None,
         None,
+        None,
     );
     assert_eq!(result.len(), 1);
 }
diff --git a/rust/src/push/mod.rs b/rust/src/push/mod.rs
index 780d7a8cbd8..19873a0bf8f 100644
--- a/rust/src/push/mod.rs
+++ b/rust/src/push/mod.rs
@@ -369,6 +369,13 @@ pub enum KnownCondition {
     SenderNotificationPermission {
         key: Cow<'static, str>,
     },
+    // MSC4506 (knock push rules): matches if the user the rules are being
+    // evaluated for has a power level at least that required to perform the
+    // action named by `key` (e.g. "invite").
+    #[serde(rename = "org.matrix.msc4506.recipient_permission")]
+    RecipientPermission {
+        key: Cow<'static, str>,
+    },
     #[serde(rename = "org.matrix.msc3931.room_version_supports")]
     RoomVersionSupports {
         feature: Cow<'static, str>,
@@ -559,6 +566,7 @@ pub struct FilteredPushRules {
     msc4028_push_encrypted_events: bool,
     msc4210_enabled: bool,
     msc4306_enabled: bool,
+    msc4506_enabled: bool,
 }
 
 #[pymethods]
@@ -574,6 +582,7 @@ impl FilteredPushRules {
         msc4028_push_encrypted_events: bool,
         msc4210_enabled: bool,
         msc4306_enabled: bool,
+        msc4506_enabled: bool,
     ) -> Self {
         Self {
             push_rules,
@@ -584,6 +593,7 @@ impl FilteredPushRules {
             msc4028_push_encrypted_events,
             msc4210_enabled,
             msc4306_enabled,
+            msc4506_enabled,
         }
     }
 
@@ -620,6 +630,11 @@ impl FilteredPushRules {
                     return false;
                 }
 
+                if !self.msc4506_enabled && rule.rule_id.contains("/.org.matrix.msc4506.rule.knock")
+                {
+                    return false;
+                }
+
                 if !self.msc4028_push_encrypted_events
                     && rule.rule_id == "global/override/.org.matrix.msc4028.encrypted_event"
                 {
diff --git a/synapse/config/experimental.py b/synapse/config/experimental.py
index f99f7b139ec..146b49a9ce5 100644
--- a/synapse/config/experimental.py
+++ b/synapse/config/experimental.py
@@ -156,6 +156,12 @@ def read_config(
             "msc3381_polls_enabled", False
         )
 
+        # MSC4506: default push rule notifying room members
+        # who can act on a knock (MSC2403), via the new `recipient_permission`
+        # push rule condition. Unstable ids: .org.matrix.msc4506.rule.knock /
+        # org.matrix.msc4506.recipient_permission.
+        self.msc4506_enabled: bool = experimental.get("msc4506_enabled", False)
+
         # MSC3912: Relation-based redactions.
         self.msc3912_enabled: bool = experimental.get("msc3912_enabled", False)
 
diff --git a/synapse/push/bulk_push_rule_evaluator.py b/synapse/push/bulk_push_rule_evaluator.py
index 03dd3417440..e6c1555c0b0 100644
--- a/synapse/push/bulk_push_rule_evaluator.py
+++ b/synapse/push/bulk_push_rule_evaluator.py
@@ -89,6 +89,19 @@
 SENTINEL = object()
 
 
+def _coerce_power_level(level: object, default: int) -> int:
+    """Interpret a power level from `m.room.power_levels` content as an
+    integer, tolerating the non-integer levels (floats, strings, nulls) that
+    old room versions permit. Falls back to `default` if uninterpretable.
+    """
+    if type(level) is int:  # noqa: E721
+        return level
+    try:
+        return int(level)  # type: ignore[call-overload]
+    except (TypeError, ValueError):
+        return default
+
+
 def _should_count_as_unread(event: EventBase, context: EventContext) -> bool:
     # Exclude rejected and soft-failed events.
     if context.rejected or event.internal_metadata.is_soft_failed():
@@ -177,6 +190,15 @@ async def _get_rules_for_event(
                 )
                 if target_already_in_room:
                     local_users = [event.state_key]
+            elif (
+                self.hs.config.experimental.msc4506_enabled
+                and event.membership == Membership.KNOCK
+            ):
+                # MSC4506: a knock (sender == state_key, so not caught above)
+                # should notify the members of the room who can act on it, so
+                # we can't take the membership-events-only-notify-their-target
+                # fast path.
+                local_users = await self.store.get_local_users_in_room(event.room_id)
         else:
             # We get the users who may need to be notified by first fetching the
             # local users currently in the room, finding those that have push rules,
@@ -458,6 +480,29 @@ async def _action_for_event_by_user(
                     except (TypeError, ValueError):
                         del notification_levels[key]
 
+        # MSC4506 (knock push rules): the level required to perform each of the
+        # room's power-levels actions, and the data to compute each recipient's
+        # own level, for the `recipient_permission` condition. As above,
+        # non-integer levels in old room versions are interpreted as integers
+        # where possible and otherwise dropped.
+        action_power_levels = {
+            "invite": power_levels.get("invite", 0),
+            "kick": power_levels.get("kick", 50),
+            "ban": power_levels.get("ban", 50),
+            "redact": power_levels.get("redact", 50),
+        }
+        for key in list(action_power_levels.keys()):
+            level = action_power_levels[key]
+            if type(level) is not int:  # noqa: E721
+                try:
+                    action_power_levels[key] = int(level)
+                except (TypeError, ValueError):
+                    del action_power_levels[key]
+        users_default_level = _coerce_power_level(
+            power_levels.get("users_default", 0), 0
+        )
+        user_power_levels = power_levels.get("users", {})
+
         # Pull out any user and room mentions.
         has_mentions = EventContentFields.MENTIONS in event.content
 
@@ -467,6 +512,7 @@ async def _action_for_event_by_user(
             room_member_count,
             sender_power_level,
             notification_levels,
+            action_power_levels,
             related_events,
             self._related_event_match_enabled,
             event.room_version.msc3931_push_features,
@@ -512,8 +558,18 @@ async def _action_for_event_by_user(
             if msc4306_thread_subscribers is not None:
                 msc4306_thread_subscription_state = uid in msc4306_thread_subscribers
 
+            # MSC4506: this user's own power level, for the
+            # `recipient_permission` condition.
+            recipient_power_level = _coerce_power_level(
+                user_power_levels.get(uid, users_default_level), users_default_level
+            )
+
             actions = evaluator.run(
-                rules, uid, display_name, msc4306_thread_subscription_state
+                rules,
+                uid,
+                display_name,
+                msc4306_thread_subscription_state,
+                recipient_power_level,
             )
             if "notify" in actions:
                 # Push rules say we should notify the user of this event
diff --git a/synapse/storage/databases/main/push_rule.py b/synapse/storage/databases/main/push_rule.py
index d361166cec4..2c06d73cbb3 100644
--- a/synapse/storage/databases/main/push_rule.py
+++ b/synapse/storage/databases/main/push_rule.py
@@ -107,6 +107,7 @@ def _load_rules(
         msc4028_push_encrypted_events=experimental_config.msc4028_push_encrypted_events,
         msc4210_enabled=experimental_config.msc4210_enabled,
         msc4306_enabled=experimental_config.msc4306_enabled,
+        msc4506_enabled=experimental_config.msc4506_enabled,
     )
 
     return filtered_rules
diff --git a/synapse/synapse_rust/push.pyi b/synapse/synapse_rust/push.pyi
index ef0d5f94f4f..344e4d3def2 100644
--- a/synapse/synapse_rust/push.pyi
+++ b/synapse/synapse_rust/push.pyi
@@ -50,6 +50,7 @@ class FilteredPushRules:
         msc4028_push_encrypted_events: bool,
         msc4210_enabled: bool,
         msc4306_enabled: bool,
+        msc4506_enabled: bool,
     ): ...
     def rules(self) -> Collection[tuple[PushRule, bool]]: ...
 
@@ -63,6 +64,7 @@ class PushRuleEvaluator:
         room_member_count: int,
         sender_power_level: int | None,
         notification_power_levels: Mapping[str, int],
+        action_power_levels: Mapping[str, int],
         related_events_flattened: Mapping[str, Mapping[str, JsonValue]],
         related_event_match_enabled: bool,
         room_version_feature_flags: list[str],
@@ -76,6 +78,7 @@ class PushRuleEvaluator:
         user_id: str | None,
         display_name: str | None,
         msc4306_thread_subscription_state: bool | None,
+        recipient_power_level: int | None = None,
     ) -> Collection[Mapping | str]: ...
     def matches(
         self,
@@ -83,4 +86,5 @@ class PushRuleEvaluator:
         user_id: str | None,
         display_name: str | None,
         msc4306_thread_subscription_state: bool | None = None,
+        recipient_power_level: int | None = None,
     ) -> bool: ...
diff --git a/tests/push/test_bulk_push_rule_evaluator.py b/tests/push/test_bulk_push_rule_evaluator.py
index 137bbe24b28..7da0215917d 100644
--- a/tests/push/test_bulk_push_rule_evaluator.py
+++ b/tests/push/test_bulk_push_rule_evaluator.py
@@ -31,7 +31,7 @@
 from synapse.api.room_versions import RoomVersions
 from synapse.push.bulk_push_rule_evaluator import BulkPushRuleEvaluator
 from synapse.rest import admin
-from synapse.rest.client import login, push_rule, register, room
+from synapse.rest.client import knock, login, push_rule, register, room
 from synapse.server import HomeServer
 from synapse.types import JsonDict, create_requester
 from synapse.util.clock import Clock
@@ -650,3 +650,82 @@ def test_with_disabled_thread_subscriptions(self) -> None:
                 type="m.room.message",
             )
         )
+
+
+class TestKnockPushRules(HomeserverTestCase):
+    """Tests for the MSC4506 knock push rule (`.org.matrix.msc4506.rule.knock`
+    with the `recipient_permission` condition): a knock should notify exactly
+    the members of the room whose power level lets them act on it.
+    """
+
+    servlets = [
+        admin.register_servlets_for_client_rest_resource,
+        room.register_servlets,
+        knock.register_servlets,
+        login.register_servlets,
+        register.register_servlets,
+        push_rule.register_servlets,
+    ]
+
+    def _knock_and_get_event_id(self) -> str:
+        """Set up a knockable room and knock on it.
+
+        Alice (PL 100, can invite) and Bob (PL 0, cannot invite: the room
+        requires PL 50) are joined; Charlie knocks. Returns the knock event id.
+        """
+        self.alice = self.register_user("alice", "pass")
+        alice_token = self.login(self.alice, "pass")
+        self.bob = self.register_user("bob", "pass")
+        bob_token = self.login(self.bob, "pass")
+        self.charlie = self.register_user("charlie", "pass")
+        charlie_token = self.login(self.charlie, "pass")
+
+        room_id = self.helper.create_room_as(
+            self.alice, is_public=True, tok=alice_token
+        )
+        self.helper.join(room_id, self.bob, tok=bob_token)
+        self.helper.send_state(
+            room_id,
+            "m.room.power_levels",
+            {"users": {self.alice: 100}, "invite": 50},
+            alice_token,
+        )
+        self.helper.send_state(
+            room_id,
+            "m.room.join_rules",
+            {"join_rule": "knock"},
+            alice_token,
+        )
+        self.helper.knock(room=room_id, user=self.charlie, tok=charlie_token)
+
+        state = self.get_success(
+            self.hs.get_storage_controllers().state.get_current_state(room_id)
+        )
+        return state[("m.room.member", self.charlie)].event_id
+
+    def _push_actions_for(self, event_id: str, user_id: str) -> list:
+        return self.get_success(
+            self.hs.get_datastores().main.db_pool.simple_select_list(
+                table="event_push_actions",
+                keyvalues={"event_id": event_id, "user_id": user_id, "notif": 1},
+                retcols=("*",),
+                desc="get_event_push_actions",
+            )
+        )
+
+    @override_config({"experimental_features": {"msc4506_enabled": True}})
+    def test_knock_notifies_only_users_who_can_act(self) -> None:
+        knock_event_id = self._knock_and_get_event_id()
+
+        # Alice can invite the knocker, so she is notified.
+        self.assertEqual(len(self._push_actions_for(knock_event_id, self.alice)), 1)
+        # Bob cannot, so he is not.
+        self.assertEqual(len(self._push_actions_for(knock_event_id, self.bob)), 0)
+        # The knocker is never notified of their own knock.
+        self.assertEqual(len(self._push_actions_for(knock_event_id, self.charlie)), 0)
+
+    def test_knock_notifies_nobody_when_disabled(self) -> None:
+        knock_event_id = self._knock_and_get_event_id()
+
+        for user_id in (self.alice, self.bob, self.charlie):
+            self.assertEqual(len(self._push_actions_for(knock_event_id, user_id)), 0)
diff --git a/tests/push/test_push_rule_evaluator.py b/tests/push/test_push_rule_evaluator.py
index 2e389710b95..c3951bde266 100644
--- a/tests/push/test_push_rule_evaluator.py
+++ b/tests/push/test_push_rule_evaluator.py
@@ -161,6 +161,7 @@ def _get_evaluator(
         content: JsonMapping,
         *,
         related_events: JsonDict | None = None,
+        action_power_levels: dict[str, int] | None = None,
         msc4210: bool = False,
         msc4306: bool = False,
     ) -> PushRuleEvaluator:
@@ -184,6 +185,7 @@ def _get_evaluator(
             room_member_count,
             sender_power_level,
             cast(dict[str, int], power_levels.get("notifications", {})),
+            {} if action_power_levels is None else action_power_levels,
             {} if related_events is None else related_events,
             related_event_match_enabled=True,
             room_version_feature_flags=event.room_version.msc3931_push_features,
@@ -820,6 +822,45 @@ def test_related_event_match_no_related_event(self) -> None:
             )
         )
 
+    def test_recipient_permission(self) -> None:
+        """
+        Test the MSC4506 `recipient_permission` condition (knock push rules).
+        """
+        evaluator = self._get_evaluator(
+            {"membership": "knock"},
+            action_power_levels={"invite": 50},
+        )
+        condition = {
+            "kind": "org.matrix.msc4506.recipient_permission",
+            "key": "invite",
+        }
+
+        # A recipient at or above the required level matches.
+        self.assertTrue(
+            evaluator.matches(condition, "@user:test", None, recipient_power_level=50)
+        )
+        self.assertTrue(
+            evaluator.matches(condition, "@user:test", None, recipient_power_level=100)
+        )
+
+        # A recipient below the required level does not match.
+        self.assertFalse(
+            evaluator.matches(condition, "@user:test", None, recipient_power_level=0)
+        )
+
+        # No recipient power level: never matches.
+        self.assertFalse(evaluator.matches(condition, "@user:test", None))
+
+        # An action key with no known level never matches.
+        self.assertFalse(
+            evaluator.matches(
+                {"kind": "org.matrix.msc4506.recipient_permission", "key": "nonsense"},
+                "@user:test",
+                None,
+                recipient_power_level=100,
+            )
+        )
+
     def test_thread_subscription_subscribed(self) -> None:
         """
         Test MSC4306 thread subscription push rules against an event in a subscribed thread.