To use pub.client:smtp with SSL you need to tune JVM first by adding the certificates in the chain to cacert file, then restart IS.
Then while in pub.client:smtp you needed to add in the properties mail.smtp.starttls.enable=true.
I had to deal once with this, but was time ago, maybe I miss some steps.
Good luck!
#webmethods-Protocol-and-Transport#Integration-Server-and-ESB#webMethods