You can forward any action from a ticket to an additional email address. This allows you to forward emails or actions to other Agents or Users for input. This will not email the user themselves unless you input their email.
This enables input form a 3rd party vendor also of whom the user is not aware, effectively segregating your commercial interests.
Forwarding is simple:
Right click on the space next to the name or action outcome.
Click on forward.
Annotate the previous parts of the thread as necessary.
Include a message to the person you're emailing.
Add their email into the To: field.
Press send to bring up the email preview screen.
Click send once you are happy with this.
This then adds a forward action to the ticket showing that a 3rd party has been consulted. Any replies from them will not be public to the end-user, but will be added to the ticket for internal viewing (under the "All Actions" view).