Debug a JavaMail Program

1. JavaMail Debug mode

To set the JavaMail Debug mode “on” :

Session mailSession = Session.getDefaultInstance(props, null);
mailSession.setDebug(true);

or set the property when launching the JVM:

java -Dmail.debug=true ...

This setting puts the JavaMail classes in debug mode mode to System.out.

To redirect the JavaMail debugging output to a more appropriate log file you can:

• Link a PrintStream to a ByteArrayOutputStream,
• Tell to JavaMail to use your PrintStream,
• Do the JavaMail stuff,
• Dump the content of the ByteArrayOutputStream to your favorite logger.

ByteArrayOutputStream os = new ByteArrayOutputStream();
   PrintStream ps = new PrintStream(os);
   Session mailSession = Session.getDefaultInstance(props, null);
   try {
     if (MAIL_DEBUG) {
        logger.info("JAVAMAIL debug mode is ON");
        mailSession.setDebug(true);
        mailSession.setDebugOut(ps);
     }
     ...
     transport.close();
     if (MAIL_DEBUG) { logger.info(os); }
   }
   finally {
     ps.close();
     os.close();
   }

2. Verify connectivity to the MailServer with Telnet:

telnet mymailserver 25

For example, you can detect if your firewall is blocking your connection.

By default, the telnet client is not installed on a Win7 workstation. To install it, open the command shell and type:

pkgmgr /iu:"TelnetClient"

You can also install it through the Control Panel, see Microsoft Technet.

Done! Happy Coding!