The default value for the From address used in jPDL mails is jbpm@noreply. The from address of mails can be configured in the jBPM configuration file jbpm.xfg.xml with key 'jbpm.mail.from.address' like this:

<jbpm-configuration>
  ...
  <string name='jbpm.mail.from.address' value='jbpm@yourcompany.com' />
</jbpm-configuration>