How to add/parse text in subject and in body text?

[Haldur Suni Johansen]

We are on Jira Software Server 7.6
The thing is, a customer sends us a case. If we assign the case to someone or comment on the matter etc. then the customer is informed of this, but at the same time the customer sends a note back on the information we have sent them. This will create a new case with us in a timely manner.
This results in a lot of new meaningless cases. We would like to stop this. The customer thinks the solution is to add/parse commands in the subject text and in the body text.
The question then is: how do I add/parse text in subject and in body text?

Example:
Case
Subject: #RequestNumber Error in Server
Body Text: There is an error in server blabla

Wanted response to customer:
Subject: RE: #RequestNumber Error in Server @@SD@@
Body Text: @@Resolution=I have checked the server blabla@@
@@Status=Closed@@

How do I solve this?