diff --git a/app/src/main/java/eu/faircode/email/ServiceSynchronize.java b/app/src/main/java/eu/faircode/email/ServiceSynchronize.java
index 9f8bbec0ca..f7d160d91a 100644
--- a/app/src/main/java/eu/faircode/email/ServiceSynchronize.java
+++ b/app/src/main/java/eu/faircode/email/ServiceSynchronize.java
@@ -993,6 +993,7 @@ public class ServiceSynchronize extends ServiceBase implements SharedPreferences
                         throw ex;
                     }
 
+                    // https://tools.ietf.org/html/rfc2177
                     final boolean capIdle = iservice.hasCapability("IDLE");
                     Log.i(account.name + " idle=" + capIdle);
                     if (!capIdle || account.poll_interval < OPTIMIZE_KEEP_ALIVE_INTERVAL)