Separate thread e-mail?

Using Comcast e-mail app/program.

Maybe I changed something and don't know what OR Comcast  changed something and I don't know why?

Previously I would write an e-mail to a friend or business. Mostly to friends it would just be chatter that one doesn't need to thread together for record quality conservation.  Now I seem to be getting all the e-mails I might send to someone back and fourth over a two day period still being threaded together even though we stopped talking about the original subject .

Is there a way I can turn this off?