I am not really sure if this works but you can try to change the [dms-service]/standalone/configuration/standalone-full-ha.xml. There is a section like this:
<mail-session name="default" jndi-name="java:jboss/mail/Default">
<remote-destination host="localhost" port="25"/>
I think that the host (and other properties) will be overwritten by the cluster configuration properties but not the port. So the default is Port 25. The attribute ssl="true" on smpt-server could be interessting and the port 465 in socket-binding.
This is also interessting to read: http://www.mastertheboss.com/jboss-server/jboss-configuration/jboss-mail-service-configuration
But I have not tried out so far. So may be we have some tasks to do... It is possible that we ignore the jboss configuration properties while sending the mails.