At the end of the two sections on running the async example are the following sentences:
"If an error occurs, the status will read Encountered an error. Check the server.log file for your domain to find the cause of the error."
If a user happens to have run the mailconnector example before they run this example, and they still have the mock-javamail JAR file in their glassfish/lib directory, the status message they see will be "javax.ejb.EJBException", and the server log stack trace will contain
SEVERE: Error in sending message.
WARNING: EJB5184:A system exception occurred during an invocation on EJB MailerBean, method: public java.util.concurrent.Future async.ejb.MailerBean.sendMessage(java.lang.String)
Caused by: java.lang.NullPointerException
I don't know if this belongs in the tutorial itself or in the FAQ – probably the latter?