Store TLS indicator

app/src/main/java/eu/faircode/email/MessageHelper.java

@@ -1936,6 +1936,9 @@ public class MessageHelper {
         // Protocol = "ESMTP" / "SMTP" / Attdl-Protocol
         // Attdl-Protocol = Atom
 
+        if (!BuildConfig.DEBUG)
+            return null;
+
         String[] received = imessage.getHeader("Received");
         if (received == null || received.length == 0)
             return null;