diff --git a/acme4j-smime/src/main/java/org/shredzone/acme4j/smime/email/EmailProcessor.java b/acme4j-smime/src/main/java/org/shredzone/acme4j/smime/email/EmailProcessor.java
index 6a76f1f2..df483666 100644
--- a/acme4j-smime/src/main/java/org/shredzone/acme4j/smime/email/EmailProcessor.java
+++ b/acme4j-smime/src/main/java/org/shredzone/acme4j/smime/email/EmailProcessor.java
@@ -305,12 +305,13 @@ public final class EmailProcessor {
      * @return {@code true} if the mail was auto-generated.
      */
     private boolean isAutoGenerated(Message message) throws MessagingException {
-        for (String header : message.getHeader("Auto-Submitted")) {
-            if (header.trim().startsWith("auto-generated")) {
-                return true;
-            }
+        String[] autoSubmitted = message.getHeader("Auto-Submitted");
+        if (autoSubmitted == null) {
+            return false;
         }
-        return false;
+        return Arrays.stream(autoSubmitted)
+                .map(String::trim)
+                .anyMatch(h -> h.startsWith("auto-generated"));
     }
 
     /**