I was wondering if it was possible to create a rule on existing requests rather than when a new one is created, to say if the subject or description on the reply or forward to that ticket contains a keyword/phrase to automatically close it?

For example in the case where a ticket was created with Request ID 765, after the ticket was created if i was then to mail the incoming mailbox from an external client like Outlook with the subject line 

RE: ##765## this can now be closed  

Is it possible to set a rule so that it scans the subject or body on the reply, look for that phrase "This can now be closed" and automatically close the ticket? 

Best Regards