One thing that always bugged me with using "replies" doesn't mean that it's a positive reply. or useful reply. seems like you could build a classifier for this.
I'm just thinking stop emailing me or unsubscribe. wrong email address. these are things that could make it look like a good reply rate but really those are useful replies at all.
Wrong email address is never counted towards to replies. The rest is correct but if you are getting that much reply with just “stop emailing”, probably there is a targeting problem.
The replies I have mentioned in the article is almost all of them are positive replies.