diff --git a/src/api/server/send.rs b/src/api/server/send.rs
index f8a5bf35..4db08758 100644
--- a/src/api/server/send.rs
+++ b/src/api/server/send.rs
@@ -32,12 +32,13 @@ use tuwunel_core::{
 	debug_warn, defer, err, error,
 	itertools::Itertools,
 	result::LogErr,
+	smallvec::SmallVec,
 	trace,
 	utils::{
-		IterStream, ReadyExt,
 		debug::str_truncated,
+		future::TryExtExt,
 		millis_since_unix_epoch,
-		stream::{BroadbandExt, TryBroadbandExt, automatic_width},
+		stream::{BroadbandExt, IterStream, ReadyExt, TryBroadbandExt, automatic_width},
 	},
 	warn,
 };
@@ -49,6 +50,9 @@ use tuwunel_service::{
 use crate::Ruma;
 
 type ResolvedMap = BTreeMap<OwnedEventId, Result>;
+type RoomsPdus = SmallVec<[RoomPdus; 1]>;
+type RoomPdus = (OwnedRoomId, TxnPdus);
+type TxnPdus = SmallVec<[(usize, Pdu); 1]>;
 type Pdu = (OwnedRoomId, OwnedEventId, CanonicalJsonObject);
 
 /// # `PUT /_matrix/federation/v1/send/{txnId}`
@@ -99,22 +103,27 @@ pub(crate) async fn send_transaction_message_route(
 		.pdus
 		.iter()
 		.stream()
-		.broad_then(|pdu| services.event_handler.parse_incoming_pdu(pdu))
-		.inspect_err(|e| debug_warn!("Could not parse PDU: {e}"))
-		.ready_filter_map(Result::ok);
+		.enumerate()
+		.broad_filter_map(|(i, pdu)| {
+			services
+				.event_handler
+				.parse_incoming_pdu(pdu)
+				.inspect_err(move |e| debug_warn!("Could not parse PDU[{i}]: {e}"))
+				.map_ok(move |pdu| (i, pdu))
+				.ok()
+		});
 
 	let edus = body
 		.edus
 		.iter()
-		.map(|edu| edu.json().get())
-		.map(serde_json::from_str)
-		.filter_map(Result::ok)
-		.stream();
-
-	trace!(
-		elapsed = ?txn_start_time.elapsed(),
-		"Parsed txn",
-	);
+		.stream()
+		.enumerate()
+		.ready_filter_map(|(i, edu)| {
+			serde_json::from_str(edu.json().get())
+				.inspect_err(|e| debug_warn!("Could not parse EDU[{i}]: {e}"))
+				.map(|edu| (i, edu))
+				.ok()
+		});
 
 	let results = handle(
 		&services,
@@ -156,8 +165,8 @@ async fn handle(
 	origin: &ServerName,
 	txn_id: &TransactionId,
 	started: Instant,
-	pdus: impl Stream<Item = Pdu> + Send,
-	edus: impl Stream<Item = Edu> + Send,
+	pdus: impl Stream<Item = (usize, Pdu)> + Send,
+	edus: impl Stream<Item = (usize, Edu)> + Send,
 ) -> Result<ResolvedMap> {
 	let results = handle_pdus(services, client, origin, txn_id, started, pdus).await?;
 
@@ -172,25 +181,24 @@ async fn handle_pdus(
 	origin: &ServerName,
 	txn_id: &TransactionId,
 	started: Instant,
-	pdus: impl Stream<Item = Pdu> + Send,
+	pdus: impl Stream<Item = (usize, Pdu)> + Send,
 ) -> Result<ResolvedMap> {
-	// group pdus by room
-	let pdus = pdus
-		.enumerate()
-		.collect()
-		.map(|mut pdus: Vec<_>| {
-			pdus.sort_by(|(_, (room_a, ..)), (_, (room_b, ..))| room_a.cmp(room_b));
+	pdus.collect()
+		.map(Ok)
+		.map_ok(|pdus: TxnPdus| {
 			pdus.into_iter()
+				.sorted_by(|(_, (room_a, ..)), (_, (room_b, ..))| room_a.cmp(room_b))
 				.into_grouping_map_by(|(_, (room_id, ..))| room_id.clone())
 				.collect()
+				.into_iter()
+				.try_stream()
 		})
-		.await;
-
-	// we can evaluate rooms concurrently
-	let results: ResolvedMap = pdus
-		.into_iter()
-		.try_stream()
-		.broad_and_then(async |(room_id, pdus): (_, Vec<_>)| {
+		.try_flatten_stream()
+		.try_collect::<RoomsPdus>()
+		.map_ok(IntoIterator::into_iter)
+		.map_ok(IterStream::try_stream)
+		.try_flatten_stream()
+		.broad_and_then(async |(room_id, pdus)| {
 			handle_room(services, client, origin, txn_id, started, room_id, pdus.into_iter())
 				.map_ok(ResolvedMap::into_iter)
 				.map_ok(IterStream::try_stream)
@@ -198,9 +206,7 @@ async fn handle_pdus(
 		})
 		.try_flatten()
 		.try_collect()
-		.await?;
-
-	Ok(results)
+		.await
 }
 
 #[tracing::instrument(
@@ -218,24 +224,24 @@ async fn handle_room(
 	ref room_id: OwnedRoomId,
 	pdus: impl Iterator<Item = (usize, Pdu)> + Send,
 ) -> Result<ResolvedMap> {
-	let _room_lock = services
+	services
 		.event_handler
 		.mutex_federation
 		.lock(room_id)
-		.await;
-
-	pdus.enumerate()
-		.try_stream()
-		.and_then(|(ri, (ti, (room_id, event_id, value)))| {
-			handle_pdu(
-				services,
-				(origin, txn_id, txn_start_time, ti),
-				(room_id, event_id, ri),
-				value,
-			)
+		.then(async |_lock| {
+			pdus.enumerate()
+				.try_stream()
+				.and_then(async |pdu| {
+					services.server.check_running().map(|()| pdu) // interruption point
+				})
+				.and_then(|(ri, (ti, (room_id, event_id, value)))| {
+					let meta = (origin, txn_id, txn_start_time, ti);
+					let pdu = (ri, (room_id, event_id, value));
+					handle_pdu(services, meta, pdu).map(Ok)
+				})
+				.try_collect()
+				.await
 		})
-		.try_collect()
-		.boxed()
 		.await
 }
 
@@ -248,11 +254,8 @@ async fn handle_room(
 async fn handle_pdu(
 	services: &Services,
 	(origin, txn_id, txn_start_time, ti): (&ServerName, &TransactionId, Instant, usize),
-	(ref room_id, event_id, ri): (OwnedRoomId, OwnedEventId, usize),
-	value: CanonicalJsonObject,
-) -> Result<(OwnedEventId, Result)> {
-	services.server.check_running()?;
-
+	(ri, (ref room_id, event_id, value)): (usize, Pdu),
+) -> (OwnedEventId, Result) {
 	let pdu_start_time = Instant::now();
 	let completed: AtomicBool = Default::default();
 	defer! {{
@@ -279,6 +282,7 @@ async fn handle_pdu(
 		.event_handler
 		.handle_incoming_pdu(origin, room_id, &event_id, value, true)
 		.map_ok(|_| ())
+		.boxed()
 		.await;
 
 	completed.store(true, Ordering::Release);
@@ -289,7 +293,7 @@ async fn handle_pdu(
 		"Finished PDU",
 	);
 
-	Ok((event_id.clone(), result))
+	(event_id.clone(), result)
 }
 
 #[tracing::instrument(name = "edus", level = "debug", skip_all)]
@@ -298,13 +302,12 @@ async fn handle_edus(
 	client: &IpAddr,
 	origin: &ServerName,
 	txn_id: &TransactionId,
-	edus: impl Stream<Item = Edu> + Send,
+	edus: impl Stream<Item = (usize, Edu)> + Send,
 ) -> Result {
-	edus.enumerate()
-		.for_each_concurrent(automatic_width(), |(i, edu)| {
-			handle_edu(services, client, origin, txn_id, i, edu)
-		})
-		.await;
+	edus.for_each_concurrent(automatic_width(), |(i, edu)| {
+		handle_edu(services, client, origin, txn_id, i, edu)
+	})
+	.await;
 
 	Ok(())
 }