and then run "newaliases" command to let sendmail know of the change. Whenever someone sends an e-mail to "jenkins-foo@yoursystem", this will trigger a new build. See this for more details about configuring sendmail.
In my case,ant default target was not being picked up from build.xml so I had to explicitly mention the target in jenkins option.I resolved this by changing the jdk to default and then again switched to what was set earlier.This is a workaround but not sure how this resolved.