This is a simple step-by-step tutorial to install and configure exim to route all e-mails send though a local SMTP server to one local user, regardless of the e-mail address or domain. I found this set-up very usefull when testing applications that send e-mail messages and you do not want to generate multiple HotMail accounts for testing or in case I'm wanted to do some testing and development when I'm offline.
While testing your JBoss service it can be very handy to use DefaultDS as your data source. However you will probably not want to hardcode this JNDI name into your code, jboss-server.xml, web.xml or persistence.xml (depending on service you write). There you want to use your own "MyAppDS" JNDI name. So wouldn't it be sweet to be able to bind two different JNDI names to the same datasource ?