diff --git a/openapi/definitions.yaml b/openapi/definitions.yaml
index eba07a2d..536b585d 100644
--- a/openapi/definitions.yaml
+++ b/openapi/definitions.yaml
@@ -97,6 +97,10 @@ MessageContentBase:
       $ref: "#/MessageSubject"
     markdown:
       $ref: "#/MessageBodyMarkdown"
+    require_secure_channels:
+      type: boolean
+      description: |-
+        When true, messages won't trigger email notifications (only push).
   required:
     - subject
     - markdown