Within Teamwork Desk, when you send a reply to a customer they will what is shown below.

When you reply to your customers, their message is automatically quoted inside of the editor (you can expand this message by clicking on this "..." icon).

You may modify or remove this quote while constructing your reply:



The message that your customer receives will be formatted identically to the message as entered within Teamwork Desk (some mail clients may apply small changes):

If you would like to quote previous replies, click the "quote message" icon and it will be included in your reply back to the customer.



Disabling quoting previous message:

If you do not wish to have the quoted text included, this feature can be turned off in Company Settings under 'Edit Company':

 

For more information see: Assigning a ticket to another Desk user