og, the reply address seems to be unique for each recipient. Mine is the same for the first part (25.10228), but the last section is a different number to yours, and so was Mrs NM's email. So I suspect they are using that as a way of tracking who is replying to their email.

But the only reason I could find for replying to the email is to unsubscribe. Otherwise all the information sections contains web URL links for further information.

I would not be concerned by the reply address. QF bought the qantas.net.au domain name a long time ago and this is a legitimate use of it in my opinion.