Within Teamwork Desk, you can use third party forwarding to connect your third party vendors into a ticket without giving them direct contact to your customers.
When you are viewing a ticket you will see a third tab called 'Forward' where you can add in the e-mail address of the third party that you wish to send the ticket to, then type your message as you normally would.
You can also assign and change the status of the ticket. When you send out the ticket your vendor will receive the ticket along with all of the previous messages in the thread.
Note: Any notes on the ticket will not be included in the forward.
You can also choose to exclude ticket history from the forward tab. If you select this option, only the message you type will be sent:
When the vendor replies to the e-mail, your customer will not be notified and the message will appear in your Teamwork Desk account as a note. (Notes are never visible to the customer).
Note: Due to restrictions on the total size of e-mails (25MB) attachments from previous messages in the ticket will be added as links into the body of the message. These files will be available download by anyone with the link and expire after 30 days.
For more information see: Setting up email forwarding in cPanel