diff -up ./Server/src/test/java/org/openas2/message/AS2MessageMDNTest.java.tests ./Server/src/test/java/org/openas2/message/AS2MessageMDNTest.java
--- ./Server/src/test/java/org/openas2/message/AS2MessageMDNTest.java.tests	2017-07-25 23:14:10.868533190 -0400
+++ ./Server/src/test/java/org/openas2/message/AS2MessageMDNTest.java	2017-07-25 23:14:46.082526670 -0400
@@ -35,6 +35,6 @@ public class AS2MessageMDNTest {
     public void shouldGenerateMessageId() throws Exception
     {
         String messageId = new AS2MessageMDN(message, false).generateMessageID();
-        assertThat("Check " + messageId, messageId.matches("^OPENAS2-[0-9]{14}\\+[0-9]{4}-[0-9]{4}@senderId_receiverId"), is(true));
+        assertThat("Check " + messageId, messageId.matches("^OPENAS2-[0-9]{14}[+-][0-9]{4}-[0-9]{4}@senderId_receiverId"), is(true));
     }
-}
\ No newline at end of file
+}