The class:
info.magnolia.module.form.processors.AbstractFormProcessor
Defines a property "enable=true" for that any form processor is triggered at all.
Besides the 'sendContactEMail' processor non of the others have a "enable=true" configured. So no confirmation mail will ever be sent.

This is also miss leading, as the dialog itself already provides a "Send a confirmation mail" checkbox, which is then checked in the processor.
But without the "enable=true" on the processor itself, this code is never reached.