The simplest way to configure the mail server is with the configuration property jbpm.mail.smtp.host in the jbpm.cfg.xml like this:

<jbpm-configuration>
  ...
  <string name="jbpm.mail.smtp.host" value="localhost" />
</jbpm-configuration>

Alternatively, when more properties need to be specified, a resource reference to a properties file can be given with the key '' like this:

<jbpm-configuration>
  ...
  <string name='resource.mail.properties' value='jbpm.mail.properties' />
</jbpm-configuration>