diff --git a/src/service/rooms/event_handler/pdu_checks.rs b/src/service/rooms/event_handler/pdu_checks.rs
index 458ff4f3b..745364f56 100644
--- a/src/service/rooms/event_handler/pdu_checks.rs
+++ b/src/service/rooms/event_handler/pdu_checks.rs
@@ -178,7 +178,7 @@ impl super::Service {
 	/// Returns a boolean indicating whether the event is authorised, and also
 	/// the resolved state before the event for later use. Returns an error if
 	/// state fetching or auth checking fails.
-	pub(super) async fn state_before_check_5(
+	pub async fn state_before_check_5(
 		&self,
 		incoming_pdu: &PduEvent,
 		room_version_rules: &RoomVersionRules,
diff --git a/src/service/rooms/membership/event.rs b/src/service/rooms/membership/event.rs
new file mode 100644
index 000000000..bcd4d4df7
--- /dev/null
+++ b/src/service/rooms/membership/event.rs
@@ -0,0 +1,84 @@
+use conduwuit::{Result, err, utils, utils::TryFutureExtExt};
+use ruma::{
+	CanonicalJsonObject, CanonicalJsonValue, OwnedUserId, RoomId, UserId,
+	canonical_json::{redact, to_canonical_value},
+	events::{
+		StateEventType,
+		room::member::{MembershipState, RoomMemberEventContent},
+	},
+	room_version_rules::RoomVersionRules,
+};
+
+impl super::Service {
+	/// Creates a membership event locally but seeds it with data from a remote
+	/// template. This means we retain total control over the created PDU, but
+	/// still use the data from the remote server that we have to blindly trust,
+	/// like auth/prev events and depth.
+	pub(super) async fn seed_local_membership_pdu(
+		&self,
+		room_id: &RoomId,
+		user_id: &UserId,
+		membership: MembershipState,
+		reason: Option<String>,
+		template: CanonicalJsonObject,
+		room_version_rules: &RoomVersionRules,
+	) -> Result<CanonicalJsonObject> {
+		// First we redact the PDU to remove any unrecognised fields.
+		let mut template = redact(template, &room_version_rules.redaction, None)
+			.map_err(|e| err!(Request(BadJson("Failed to redact membership template: {e:?}"))))?;
+
+		// Remove fields that are not necessary but not covered by redaction.
+		template.remove("event_id");
+		template.remove("hashes");
+		template.remove("prev_state");
+		template.remove("origin");
+		template.remove("membership");
+		template.remove("redacts");
+
+		// Force set some fields to known good values.
+		let join_authorized_via_users_server = {
+			if room_version_rules
+				.signatures
+				.check_join_authorised_via_users_server
+			{
+				template
+					.get("content")
+					.map(|s| {
+						s.as_object()?
+							.get("join_authorised_via_users_server")?
+							.as_str()
+					})
+					.and_then(|s| OwnedUserId::try_from(s.unwrap_or_default()).ok())
+			} else {
+				None
+			}
+		};
+
+		let mut content = RoomMemberEventContent::new(membership);
+		let (dn, av) = tokio::join!(
+			self.services.users.displayname(user_id).ok(),
+			self.services.users.avatar_url(user_id).ok()
+		);
+		content.displayname = dn;
+		content.avatar_url = av;
+		content.reason = reason;
+		content
+			.join_authorized_via_users_server
+			.clone_from(&join_authorized_via_users_server);
+		template.insert("content".to_owned(), to_canonical_value(content)?);
+		template.insert(
+			"origin_server_ts".to_owned(),
+			CanonicalJsonValue::Integer(
+				utils::millis_since_unix_epoch()
+					.try_into()
+					.expect("Timestamp is valid js_int value"),
+			),
+		);
+		template.insert("room_id".to_owned(), room_id.as_str().into());
+		template.insert("sender".to_owned(), user_id.to_string().into());
+		template.insert("state_key".to_owned(), user_id.to_string().into());
+		template.insert("type".to_owned(), StateEventType::RoomMember.to_string().into());
+
+		Ok(template)
+	}
+}
diff --git a/src/service/rooms/membership/join.rs b/src/service/rooms/membership/join.rs
new file mode 100644
index 000000000..0bdadfd22
--- /dev/null
+++ b/src/service/rooms/membership/join.rs
@@ -0,0 +1,751 @@
+use std::{
+	borrow::Borrow,
+	collections::{BTreeMap, HashMap},
+	sync::Arc,
+	time::Instant,
+};
+
+use assign::assign;
+use conduwuit::{
+	Err, Event, PduEvent, Result, debug, debug_error, debug_info, err, error, info,
+	matrix::StateKey,
+	state_res,
+	state_res::EventTypeExt,
+	trace,
+	utils::{
+		IterStream,
+		stream::{BroadbandExt, WidebandExt, automatic_width},
+	},
+	warn,
+};
+use futures::{StreamExt, future::ready};
+use ruma::{
+	CanonicalJsonObject, EventId, OwnedEventId, OwnedRoomId, RoomId, RoomVersionId, ServerName,
+	UserId,
+	api::{
+		error::{ErrorKind, IncompatibleRoomVersionErrorData},
+		federation::membership::{create_join_event, prepare_join_event},
+	},
+	events::{StateEventType, room::member::MembershipState},
+	room_version_rules::RoomVersionRules,
+};
+use serde_json::value::to_raw_value;
+
+use crate::rooms::{
+	event_handler::{DagBuilderTree, build_local_dag},
+	membership::validate_remote_member_event_stub,
+	state::RoomMutexGuard,
+	state_compressor::{CompressedState, HashSetCompressStateEvent},
+};
+
+type StateTypeKey = (StateEventType, StateKey);
+
+pub enum MakeJoinResult {
+	/// A make_join request returned and the response was validated
+	/// successfully.
+	Success((CanonicalJsonObject, RoomVersionId)),
+	/// A make_join response indicated further attempts to join should not be
+	/// made (e.g. Forbidden).
+	Fatal(conduwuit::Error),
+	/// A make_join request failed (e.g. remote server unreachable, or unable to
+	/// fulfill restricted join requirements), but another join attempt through
+	/// another remote should be attempted.
+	Retry,
+}
+
+fn state_key_from_json(obj: &CanonicalJsonObject) -> Option<(StateEventType, StateKey)> {
+	let event_type = StateEventType::from(obj.get("type")?.as_str()?);
+	let state_key = StateKey::from_str(obj.get("state_key")?.as_str()?);
+	Some((event_type, state_key))
+}
+
+impl super::Service {
+	/// Performs `POST /_matrix/federation/v1/make_join/{room_id}/{user_id}`.
+	///
+	/// If the request is successful, the resulting template is validated to
+	/// ensure the remote server isn't returning a bad event, and then the
+	/// template and room version are returned.
+	/// If validation fails, `Ok(None)` is returned, in
+	///
+	/// If the request is unsuccessful, either an `Err` or `Ok(None)` will be
+	/// returned, depending on the reason for the failure. If the join loop
+	/// should terminate (for example, a `M_FORBIDDEN` error was returned,
+	/// indicating we cannot join), then an `Err` will be returned. If the join
+	/// loop should continue because the request failed due to conditional
+	/// problems (e.g. server offline or unable to grant join), then `Ok(None)`
+	/// will be returned.
+	pub async fn make_join(
+		&self,
+		room_id: &RoomId,
+		user_id: &UserId,
+		via: &ServerName,
+	) -> MakeJoinResult {
+		assert!(
+			self.services.globals.user_is_local(user_id),
+			"can only make_join for local users"
+		);
+
+		let request = assign!(
+			prepare_join_event::v1::Request::new(room_id.to_owned(), user_id.to_owned()),
+			{ ver: self.services.server.supported_room_versions().collect() }
+		);
+
+		info!("Asking {via} for make_join");
+		let make_join_response = self
+			.services
+			.sending
+			.send_federation_request(via, request)
+			.await
+			.inspect(|_| info!("{via} finished make_join successfully"))
+			.inspect_err(|e| debug_info!("{via} failed to make_join: {e:?}"));
+
+		let make_join_response = match make_join_response {
+			| Ok(r) => r,
+			| Err(e) => return Self::handle_make_join_error(room_id, via, e),
+		};
+
+		// Make sure the remote server hasn't sent us garbage
+		let Ok(template) = serde_json::from_str(make_join_response.event.get())
+			.inspect_err(|e| warn!("{via} returned an invalid membership template: {e}"))
+		else {
+			return MakeJoinResult::Retry;
+		};
+		if let Err(e) =
+			validate_remote_member_event_stub(&MembershipState::Join, user_id, room_id, &template)
+		{
+			warn!("{via} returned an illegal membership template event: {e:?}");
+			return MakeJoinResult::Retry;
+		}
+
+		MakeJoinResult::Success((
+			template,
+			make_join_response.room_version.unwrap_or(RoomVersionId::V1),
+		))
+	}
+
+	/// Handles an error response from make_join, determining whether it should
+	/// be fatal (and returning `MakeJoinResult::Fatal(e)`), or
+	/// temporary/situational and returning `MakeJoinResult::Retry`.
+	fn handle_make_join_error(
+		room_id: &RoomId,
+		via: &ServerName,
+		e: conduwuit::Error,
+	) -> MakeJoinResult {
+		match e.kind() {
+			| ErrorKind::UnableToAuthorizeJoin => {
+				info!(
+					"{via} was unable to verify the joining user satisfied restricted join \
+					 requirements: {e}."
+				);
+				MakeJoinResult::Retry
+			},
+			| ErrorKind::UnableToGrantJoin => {
+				info!(
+					"{via} believes the joining user satisfies restricted join rules, but is \
+					 unable to authorise a join for us."
+				);
+				MakeJoinResult::Retry
+			},
+			| ErrorKind::IncompatibleRoomVersion(IncompatibleRoomVersionErrorData {
+				room_version,
+				..
+			}) => {
+				warn!(
+					"{via} reports the room we are trying to join is v{room_version}, which we \
+					 do not support."
+				);
+				MakeJoinResult::Fatal(e)
+			},
+			| ErrorKind::Forbidden => {
+				warn!("{via} refuses to let us join: {e}.");
+				MakeJoinResult::Fatal(e)
+			},
+			| ErrorKind::NotFound => {
+				info!("{via} does not know about {room_id}: {e}.");
+				MakeJoinResult::Retry
+			},
+			| ErrorKind::Unknown if e.status_code().is_server_error() => {
+				match e.status_code() {
+					| http::StatusCode::BAD_GATEWAY | http::StatusCode::SERVICE_UNAVAILABLE =>
+						info!("{via} is unavailable: {e}"),
+					| http::StatusCode::GATEWAY_TIMEOUT =>
+						info!("{via} timed out while handling make_join: {e}"),
+					| _ => info!("{via} encountered an internal server error: {e}."),
+				}
+				MakeJoinResult::Retry
+			},
+			| _ => {
+				info!("{via} unexpectedly failed to make_join: {e}.");
+				MakeJoinResult::Retry
+			},
+		}
+	}
+
+	async fn send_join(
+		&self,
+		room_id: OwnedRoomId,
+		event_id: OwnedEventId,
+		event: CanonicalJsonObject,
+		via: &ServerName,
+		room_version_rules: &RoomVersionRules,
+		state_lock: &RoomMutexGuard,
+	) -> Result {
+		let send_join_request = create_join_event::v2::Request::new(
+			room_id.clone(),
+			event_id.clone(),
+			self.services
+				.sending
+				.convert_to_outgoing_federation_event(event.clone())
+				.await,
+		);
+
+		info!("Asking {via} for send_join in room {room_id}");
+		self.services
+			.short
+			.get_or_create_shortroomid(&room_id)
+			.await;
+		let send_join_response = self
+			.services
+			.sending
+			.send_slow_federation_request(via, send_join_request)
+			.await
+			.inspect(|resp| {
+				info!(
+					"{via} finished send_join successfully, returning {} state events and {} \
+					 authentication events.",
+					resp.room_state.state.len(),
+					resp.room_state.auth_chain.len(),
+				);
+			})
+			.inspect_err(|e| debug_error!("{via} failed to send_join: {e:?}"))?;
+
+		info!("Acquiring server signing keys for room state events");
+		self.services
+			.server_keys
+			.acquire_events_pubkeys(
+				send_join_response
+					.room_state
+					.state
+					.iter()
+					.chain(send_join_response.room_state.auth_chain.iter()),
+			)
+			.await;
+
+		info!("Building state map");
+		let (create_event, untrusted_state_before) = self
+			.build_state_map(&send_join_response, &room_id, room_version_rules)
+			.await?;
+
+		info!(
+			"Handling returned room state authentication events ({} events)",
+			send_join_response.room_state.auth_chain.len()
+		);
+		let auth_map = self
+			.process_send_join_auth_chain(
+				&send_join_response,
+				&room_id,
+				room_version_rules,
+				&create_event,
+			)
+			.await?;
+
+		info!("Handling returned room state ({} events)", untrusted_state_before.len());
+		let untrusted_state_before_by_id = untrusted_state_before
+			.values()
+			.map(|value| {
+				(
+					value
+						.get("event_id")
+						.and_then(|v| v.as_str())
+						.and_then(|v| EventId::parse(v).ok())
+						.expect("We inserted event_id during parsing"),
+					value,
+				)
+			})
+			.collect::<HashMap<_, _>>();
+		let state_before = self
+			.process_send_join_state(
+				untrusted_state_before_by_id,
+				&auth_map,
+				room_version_rules,
+				&create_event,
+			)
+			.await?;
+		let state_before_by_id = state_before
+			.values()
+			.map(|value| (value.event_id().to_owned(), value))
+			.collect::<HashMap<_, _>>();
+
+		info!("Authorizing join event");
+		let final_membership_event =
+			if let Some(event) = send_join_response.room_state.event.as_ref() {
+				event
+			} else {
+				&to_raw_value(&event)
+					.expect("must be able to convert CanonicalJsonObject to RawJsonValue")
+			};
+
+		let (membership_pdu, membership_pdu_json) = self
+			.process_send_join_membership_event(
+				final_membership_event,
+				&event_id,
+				&state_before,
+				&state_before_by_id,
+				room_version_rules,
+			)
+			.await?;
+
+		// We've successfully joined now, and can update our local state cache.
+		info!("Compressing resolved state");
+		let compressed_state_map = state_before
+			.into_iter()
+			.stream()
+			.broad_filter_map(|(key, pdu)| async move {
+				let ssk = self
+					.services
+					.short
+					.get_or_create_shortstatekey(&key.0, key.1.as_str())
+					.await;
+				Some((ssk, pdu.event_id.clone()))
+			})
+			.collect::<Vec<_>>()
+			.await;
+		let compressed: CompressedState = self
+			.services
+			.state_compressor
+			.compress_state_events(
+				compressed_state_map
+					.iter()
+					.map(|(ssk, eid)| (ssk, eid.borrow())),
+			)
+			.collect()
+			.await;
+
+		debug!("Saving compressed state");
+		let HashSetCompressStateEvent {
+			shortstatehash: statehash_before_join,
+			added,
+			removed,
+		} = self
+			.services
+			.state_compressor
+			.save_state(&room_id, Arc::new(compressed))
+			.await?;
+
+		debug!("Updating state cache");
+		self.services
+			.state
+			.force_state(&room_id, statehash_before_join, added, removed, state_lock)
+			.await?;
+
+		debug!("Promoting membership event");
+		self.services
+			.timeline
+			.append_pdu(
+				&membership_pdu,
+				membership_pdu_json,
+				std::iter::once(membership_pdu.event_id()),
+				state_lock,
+				&room_id,
+			)
+			.await
+			.inspect(|_| info!("Finished joining {room_id}"))
+			.map(|_| ())
+	}
+
+	async fn build_state_map(
+		&self,
+		response: &create_join_event::v2::Response,
+		room_id: &RoomId,
+		room_version_rules: &RoomVersionRules,
+	) -> Result<(PduEvent, HashMap<StateTypeKey, CanonicalJsonObject>)> {
+		// NOTE: this is untrusted as we haven't performed any of the PDU checks yet.
+		// Events in this map should not be persisted blindly.
+		let untrusted_state_before = response
+			.room_state
+			.state
+			.iter()
+			.stream()
+			.wide_filter_map(async |pdu| {
+				let (event_room_id, event_id, mut value) = self
+					.services
+					.event_handler
+					.parse_incoming_pdu(pdu, Some(room_version_rules))
+					.await
+					.inspect_err(|e| warn!("Invalid PDU in room state (dropping): {e:?}"))
+					.ok()?;
+				value.insert("event_id".to_owned(), event_id.as_str().into());
+				if event_room_id != room_id {
+					warn!(%event_id, expected=%room_id, actual=%event_room_id, "PDU in room state belongs to a different room (dropping)");
+					return None;
+				}
+				if self.services.pdu_metadata.is_event_rejected(&event_id).await {
+					// Rejection will be re-evaluated later
+					trace!(%event_id, "Un-rejecting event");
+					self.services.pdu_metadata.unmark_event_rejected(&event_id);
+				}
+				Some((state_key_from_json(&value)?, value))
+			})
+			.collect::<HashMap<(StateEventType, StateKey), CanonicalJsonObject>>()
+			.await;
+
+		let create_event: PduEvent = serde_json::from_value(serde_json::to_value(
+			untrusted_state_before
+				.get(&StateEventType::RoomCreate.with_state_key(""))
+				.ok_or_else(|| {
+					err!("Room state returned from send_join did not contain a room create event")
+				})?,
+		)?)?;
+
+		Ok((create_event, untrusted_state_before))
+	}
+
+	async fn process_send_join_auth_chain(
+		&self,
+		response: &create_join_event::v2::Response,
+		room_id: &RoomId,
+		room_version_rules: &RoomVersionRules,
+		create_event: &PduEvent,
+	) -> Result<BTreeMap<OwnedEventId, PduEvent>> {
+		let auth_chain_timing_start = Instant::now();
+		let unauthed_auth_chain = response
+			.room_state
+			.auth_chain
+			.iter()
+			.stream()
+			.broad_filter_map(|value| async move {
+				self
+					.services
+					.event_handler
+					.parse_incoming_pdu(
+						&to_raw_value(&value)
+							.expect("CanonicalJsonObject just convert to RawJsonValue"),
+						Some(room_version_rules),
+					)
+					.await
+					.inspect_err(|e| warn!("Invalid PDU in send_join auth chain (dropping): {e:?}"))
+					.ok()
+			})
+			.broad_filter_map(|(auth_room_id, event_id, value)| async move {
+				if self.services.pdu_metadata.is_event_rejected(&event_id).await {
+					// Rejection will be re-evaluated later
+					trace!(%event_id, "Un-rejecting event");
+					self.services.pdu_metadata.unmark_event_rejected(&event_id);
+				}
+				trace!(%event_id, "Validating event");
+				if auth_room_id != room_id {
+					warn!(%event_id, %room_id, %auth_room_id, "PDU in send_join auth chain belongs to a different room (dropping)");
+					return None;
+				}
+
+				crate::rooms::event_handler::Service::pdu_format_check_1(&value, room_version_rules, create_event.event_id()).inspect_err(|e| {
+					warn!(%event_id, "PDU in send_join auth chain failed format check (dropping): {e:?}");
+				}).ok()?;
+
+				let value = self.services.event_handler.signature_hash_check_2_3(value, room_version_rules).await.inspect_err(|e| {
+					warn!(%event_id, "PDU in send_join auth chain failed signature check (dropping): {e:?}");
+				}).ok()?;
+
+				Some((event_id, value))
+			})
+			.collect::<HashMap<_, _>>()
+			.await;
+		debug!(
+			elapsed=?auth_chain_timing_start.elapsed(),
+			"Finished validating auth chain ({}/{} events passed validation)",
+			unauthed_auth_chain.len(),
+			response.room_state.auth_chain.len()
+		);
+		let auth_chain = build_local_dag(&unauthed_auth_chain, DagBuilderTree::AuthEvents)
+			.await?
+			.into_iter()
+			.stream()
+			.wide_filter_map(async |event_id| {
+				// Perform PDU check 4 to make sure the event doesn't need
+				// rejecting
+				let pdu =
+					PduEvent::from_id_val(&event_id, unauthed_auth_chain[&event_id].clone())
+						.expect("We already validated auth chian PDUs");
+				let auth_state = pdu
+					.auth_events()
+					.filter_map(|event_id| {
+						PduEvent::from_id_val(
+							event_id,
+							unauthed_auth_chain.get(event_id)?.clone(),
+						)
+						.map(|pdu| {
+							Some((
+								pdu.kind().with_state_key(
+									pdu.state_key()
+										.expect("Auth chain events must have a state key"),
+								),
+								pdu,
+							))
+						})
+						.ok()?
+					})
+					.collect::<HashMap<_, _>>();
+				self.services
+					.event_handler
+					.auth_state_check_4(
+						&pdu,
+						room_version_rules,
+						create_event.as_pdu(),
+						&auth_state,
+					)
+					.await
+					.inspect(|result| {
+						if !*result {
+							// NOTE: usually we don't *drop* events that fail PDU check 4, but
+							// send_join handling is special. Instead of rejecting this event and
+							// consequently every other event that depends on it, we simply drop
+							// it from the chain
+							warn!(%event_id, "Auth chain event failed self-authorization (dropping)");
+						}
+					})
+					.inspect_err(
+						|e| error!(%event_id, ?e, "Failed to run auth check on auth chain event"),
+					)
+					.unwrap_or_default()
+					.then_some((event_id, pdu))
+			})
+			.collect::<BTreeMap<_, _>>()
+			.await;
+		debug!(
+			elapsed=?auth_chain_timing_start.elapsed(),
+			"Finished authentication auth chain ({}/{} events passed authentication)",
+			auth_chain.len(),
+			unauthed_auth_chain.len()
+		);
+		// Now we need to persist them
+		auth_chain
+			.keys()
+			.stream()
+			.for_each_concurrent(automatic_width(), async |event_id| {
+				if self.services.timeline.get_pdu(event_id).await.is_err() {
+					// Only add events that we don't already have
+					self.services.outlier.add_pdu_outlier(
+						event_id,
+						unauthed_auth_chain
+							.get(event_id)
+							.expect("authorized auth chain event must be in auth chain map"),
+					);
+				}
+			})
+			.await;
+		info!(elapsed=?auth_chain_timing_start.elapsed(), "Finished processing authentication events");
+
+		Ok(auth_chain)
+	}
+
+	async fn process_send_join_state(
+		&self,
+		untrusted_state_before: HashMap<OwnedEventId, &CanonicalJsonObject>,
+		auth_chain: &BTreeMap<OwnedEventId, PduEvent>,
+		room_version_rules: &RoomVersionRules,
+		create_event: &PduEvent,
+	) -> Result<HashMap<StateTypeKey, PduEvent>> {
+		let state_timing_start = Instant::now();
+		let state_size = untrusted_state_before.len();
+		// NOTE: unlike the auth chain, we need to run PDU checks 1 through 4.
+		let state_before = untrusted_state_before
+			.into_iter()
+			.stream()
+			.broad_filter_map(|(event_id, value)| async move {
+				crate::rooms::event_handler::Service::pdu_format_check_1(
+					value,
+					room_version_rules,
+					create_event.event_id(),
+				)
+				.inspect_err(|e| {
+					warn!(%event_id, "PDU in send_join state failed format check (dropping): {e:?}");
+				})
+				.ok()?;
+
+				let value = self
+					.services
+					.event_handler
+					.signature_hash_check_2_3(value.clone(), room_version_rules)
+					.await
+					.inspect_err(|e| {
+						warn!(%event_id, "PDU in send_join state failed signature check (dropping): {e:?}");
+					})
+					.ok()?;
+
+				let pdu = PduEvent::from_id_val(&event_id, value.clone())
+					.expect("We already validated this state event");
+				let auth_state = pdu
+					.auth_events()
+					.filter_map(|event_id| {
+						auth_chain.get(event_id).map(|p| {
+							(
+								p.kind().with_state_key(
+									p.state_key()
+										.expect("auth chain events must have a state key"),
+								),
+								p.clone(),
+							)
+						})
+					})
+					.collect::<HashMap<_, _>>();
+				self.services
+					.event_handler
+					.auth_state_check_4(
+						&pdu,
+						room_version_rules,
+						create_event.as_pdu(),
+						&auth_state,
+					)
+					.await
+					.inspect(|result| {
+						if !*result {
+							warn!(%event_id, "State event failed self-authorization (dropping)");
+						}
+					})
+					.inspect_err(
+						|e| error!(%event_id, ?e, "Failed to run auth check on state event"),
+					)
+					.unwrap_or_default()
+					.then_some((pdu, value))
+			})
+			.collect::<Vec<_>>()
+			.await;
+		debug!(
+			elapsed=?state_timing_start.elapsed(),
+			"Finished validation and authentication of room state ({}/{} events retained)",
+			state_before.len(),
+			state_size,
+		);
+
+		state_before
+			.iter()
+			.stream()
+			.for_each_concurrent(automatic_width(), async |(pdu, pdu_json)| {
+				if self
+					.services
+					.timeline
+					.get_pdu(pdu.event_id())
+					.await
+					.is_err()
+				{
+					// Only add events that we don't already have
+					self.services
+						.outlier
+						.add_pdu_outlier(pdu.event_id(), pdu_json);
+				}
+			})
+			.await;
+
+		info!(
+			elapsed=?state_timing_start.elapsed(),
+			"Finished processing send join state ({}/{} events)",
+			state_before.len(),
+			state_size,
+		);
+
+		let state_before_by_key = state_before
+			.into_iter()
+			.map(|(pdu, _)| {
+				(
+					pdu.kind().with_state_key(
+						pdu.state_key().expect("state event must have a state key"),
+					),
+					pdu,
+				)
+			})
+			.collect::<HashMap<_, _>>();
+
+		Ok(state_before_by_key)
+	}
+
+	async fn process_send_join_membership_event(
+		&self,
+		membership_event: &serde_json::value::RawValue,
+		event_id: &EventId,
+		state_before: &HashMap<StateTypeKey, PduEvent>,
+		state_before_by_id: &HashMap<OwnedEventId, &PduEvent>,
+		room_version_rules: &RoomVersionRules,
+	) -> Result<(PduEvent, CanonicalJsonObject)> {
+		let (_, calculated_event_id, value) = self
+			.services
+			.event_handler
+			.parse_incoming_pdu(membership_event, Some(room_version_rules))
+			.await?;
+
+		if calculated_event_id != event_id {
+			return Err!(Request(InvalidParam(debug_warn!(
+				expected=%event_id,
+				actual=%calculated_event_id,
+				"Remote server returned a different membership event to the one we sent it"
+			))));
+		}
+
+		if self.services.pdu_metadata.is_event_rejected(event_id).await {
+			// Rejection will be re-evaluated later
+			trace!(%event_id, "Un-rejecting event");
+			self.services.pdu_metadata.unmark_event_rejected(event_id);
+		}
+
+		let create_event = state_before
+			.get(&StateEventType::RoomCreate.with_state_key(""))
+			.expect("create event must be in state before");
+		crate::rooms::event_handler::Service::pdu_format_check_1(
+			&value,
+			room_version_rules,
+			create_event.event_id(),
+		)?;
+
+		let value = self
+			.services
+			.event_handler
+			.signature_hash_check_2_3(value, room_version_rules)
+			.await?;
+
+		let pdu = PduEvent::from_id_val(event_id, value.clone())
+			.expect("We already validated this state event");
+
+		// Perform check 4 to make sure the PDU is self-authorised
+		let auth_state = pdu
+			.auth_events()
+			.filter_map(|event_id| {
+				state_before_by_id
+					.get(event_id)
+					.copied()
+					.map(|p| (p.kind().with_state_key(p.state_key().unwrap()), p.clone()))
+			})
+			.collect::<HashMap<_, _>>();
+		if !self
+			.services
+			.event_handler
+			.auth_state_check_4(&pdu, room_version_rules, create_event.as_pdu(), &auth_state)
+			.await?
+		{
+			return Err!(Request(Forbidden("Membership event was not self-authorised")));
+		}
+
+		// We can also perform check 5 (state before), since the state returned in the
+		// response is the state just before our join. However, state_before_check_5
+		// (part of the event_handler service) won't understand this, so we have to do
+		// the check manually.
+		let state_fetch =
+			|k: StateEventType, s: StateKey| ready(state_before.get(&(k, s)).cloned());
+
+		// PDU check: 5
+		let auth_check = state_res::event_auth::auth_check(
+			room_version_rules,
+			&pdu,
+			None, // TODO: third party invite
+			|ty, sk| state_fetch(ty.clone(), sk.into()),
+			create_event.as_pdu(),
+		)
+		.await
+		.map_err(|e| err!(Request(Forbidden("Auth check failed: {e:?}"))))?;
+		if !auth_check {
+			return Err!(Request(Forbidden(
+				"Membership event was not authorised based on the state before it"
+			)));
+		}
+
+		Ok((pdu, value))
+	}
+}
diff --git a/src/service/rooms/membership/mod.rs b/src/service/rooms/membership/mod.rs
index 0f8b816e5..ae11c8767 100644
--- a/src/service/rooms/membership/mod.rs
+++ b/src/service/rooms/membership/mod.rs
@@ -1,3 +1,6 @@
+mod event;
+mod join;
+
 use std::{collections::HashMap, sync::Arc};
 
 use conduwuit::{