diff --git a/docker-compose.yml b/docker-compose.yml
index 7de4e402e..d7c306b7c 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -34,7 +34,8 @@ services:
       DEBUG: "True"
       REDIS_HOST: redis
     command: >
-      sh -c "cd test_project
+      sh -c "redis-server &
+             cd test_project
              python3 manage.py migrate
              python3 manage.py load_initial_data
              django-admin compilemessages
diff --git a/frontend/src/components/identities/AccountMailboxForm.vue b/frontend/src/components/identities/AccountMailboxForm.vue
index 06fd0a8db..6e69a0347 100644
--- a/frontend/src/components/identities/AccountMailboxForm.vue
+++ b/frontend/src/components/identities/AccountMailboxForm.vue
@@ -24,15 +24,21 @@
       />
   </validation-provider>
   <label class="m-label">{{ $gettext('Daily message sending limit') }}</label>
-  <v-text-field
-    v-model="form.mailbox.message_limit"
-    :placeholder="'Leave empty for no limit' | translate"
-    :hint="'Number of messages this mailbox can send per day. Leave empty for no limit.' | translate"
-    persistent-hint
-    outlined
-    dense
-    @input="update"
-    />
+  <validation-provider
+    v-slot="{ errors }"
+    rules="numeric"
+    >
+    <v-text-field
+      v-model="form.mailbox.message_limit"
+      :placeholder="'Leave empty for no limit' | translate"
+      :hint="'Number of messages this mailbox can send per day. Leave empty for no limit.' | translate"
+      persistent-hint
+      outlined
+      dense
+      :error-messages="errors"
+      @input="update"
+      />
+  </validation-provider>
 </validation-observer>
 </template>
 
@@ -94,6 +100,9 @@ export default {
         if (this.form.role === 'SimpleUsers') {
           this.$set(this.form.mailbox, 'full_address', this.form.username)
         }
+        if (newValue.mailbox.message_limit === '') {
+          this.form.mailbox.message_limit = null
+        }
       },
       deep: true
     }
diff --git a/modoboa/admin/api/v1/serializers.py b/modoboa/admin/api/v1/serializers.py
index 418630a51..d735455df 100644
--- a/modoboa/admin/api/v1/serializers.py
+++ b/modoboa/admin/api/v1/serializers.py
@@ -152,9 +152,6 @@ class MailboxSerializer(serializers.ModelSerializer):
     quota = serializers.CharField(required=False)
     quota_usage = serializers.SerializerMethodField()
 
-    message_limit = serializers.CharField(
-            required=False, allow_null=True, allow_blank=True)
-
     class Meta:
         model = models.Mailbox
         fields = (
@@ -169,14 +166,6 @@ class MailboxSerializer(serializers.ModelSerializer):
         """Lower case address."""
         return value.lower()
 
-    def validate_message_limit(self, value):
-        if not value:
-            return None
-        try:
-            return int(value)
-        except ValueError:
-            raise ValidationError(_("A valid integer is required."))
-
     def validate_quota(self, value):
         """Convert quota to MB."""
         return web_utils.size2integer(value, output_unit="MB")
diff --git a/modoboa/admin/api/v2/serializers.py b/modoboa/admin/api/v2/serializers.py
index cd256e4e4..4e0cec594 100644
--- a/modoboa/admin/api/v2/serializers.py
+++ b/modoboa/admin/api/v2/serializers.py
@@ -389,9 +389,6 @@ class MailboxSerializer(serializers.ModelSerializer):
 
     quota = serializers.CharField(required=False)
 
-    message_limit = serializers.CharField(
-            required=False, allow_null=True, allow_blank=True)
-
     class Meta:
         model = models.Mailbox
         fields = (
@@ -402,14 +399,6 @@ class MailboxSerializer(serializers.ModelSerializer):
         """Convert quota to MB."""
         return web_utils.size2integer(value, output_unit="MB")
 
-    def validate_message_limit(self, value):
-        if value == "":
-            return None
-        try:
-            return int(value)
-        except ValueError:
-            raise ValidationError(_("A valid integer is required."))
-
     def validate(self, data):
         """Check if quota is required."""
         method = self.context["request"].method