Recognize nullmailer

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

@@ -3195,6 +3195,7 @@ public class MessageHelper {
         // (qmail nnn invoked by uid nnn); 1 Jan 2022 00:00:00 -0000
         // Postfix: by <host name> (<name>, from userid nnn)
         if (header.matches(".*\\(qmail \\d+ invoked by uid \\d+\\).*") ||
+                header.matches(".*\\(nullmailer pid \\d+ invoked by uid \\d+\\).*") ||
                 header.matches(".*\\(.*, from userid \\d+\\).*")) {
             Log.i("--- phrase");
             return true;