diff --git a/bot/bot.go b/bot/bot.go
index 83826be..56d25c8 100644
--- a/bot/bot.go
+++ b/bot/bot.go
@@ -22,6 +22,7 @@ type Bot struct {
 	rooms                   sync.Map
 	log                     *logger.Logger
 	lp                      *linkpearl.Linkpearl
+	mu                      map[id.RoomID]*sync.Mutex
 	handledMembershipEvents sync.Map
 }
 
@@ -35,6 +36,7 @@ func New(lp *linkpearl.Linkpearl, log *logger.Logger, prefix, domain string, noo
 		rooms:      sync.Map{},
 		log:        log,
 		lp:         lp,
+		mu:         map[id.RoomID]*sync.Mutex{},
 	}
 }
 
diff --git a/bot/email.go b/bot/email.go
index e4849af..b82f9d5 100644
--- a/bot/email.go
+++ b/bot/email.go
@@ -49,6 +49,8 @@ func (b *Bot) Send(ctx context.Context, email *utils.Email) error {
 	if !ok {
 		return errors.New("room not found")
 	}
+	b.lock(roomID)
+	defer b.unlock(roomID)
 
 	cfg, err := b.getSettings(roomID)
 	if err != nil {
diff --git a/bot/mutext.go b/bot/mutext.go
new file mode 100644
index 0000000..8bc091d
--- /dev/null
+++ b/bot/mutext.go
@@ -0,0 +1,26 @@
+package bot
+
+import (
+	"sync"
+
+	"maunium.net/go/mautrix/id"
+)
+
+func (b *Bot) lock(roomID id.RoomID) {
+	_, ok := b.mu[roomID]
+	if !ok {
+		b.mu[roomID] = &sync.Mutex{}
+	}
+
+	b.mu[roomID].Lock()
+}
+
+func (b *Bot) unlock(roomID id.RoomID) {
+	_, ok := b.mu[roomID]
+	if !ok {
+		return
+	}
+
+	b.mu[roomID].Unlock()
+	delete(b.mu, roomID)
+}
diff --git a/e2e/send-stress b/e2e/send-stress
new file mode 100755
index 0000000..e4b5da9
--- /dev/null
+++ b/e2e/send-stress
@@ -0,0 +1,8 @@
+#!/bin/bash
+
+for i in {0..10..1}; do
+	echo "#${i}..."
+	ssmtp test@localhost < $1
+done
+
+echo "done"