Is there a way to configure a response to a ticket NOT create a new ticket with RE: (whatever the email subject is)

 

Ex.

Client sends in an email for support as ticket #1 > agent responds > client responds back and it now created ticket #2 Re: (whatever email subject is)

This should not happen as long as they don't modify the subject line besides the added RE:, you need to reach out to support as something is wrong.