Notifications for replies should be off by default

It seems like people are more likely to use the reply feature simply as a way to indicate which message they are responding to, rather than specifically using the reply feature to notify the person they are responding to. In this case, it makes more sense for the notification to be off by default.

This means that the user must actively choose to notify the other person--but if they happen to not turn the notification on, they can simply send a follow-up message with an @ notification. Compare this with the user having to actively choose to not notify the other person--if they forget to do so, the notification has already been sent and they can't un-notify the other person.

Perhaps this could even be a user setting that can allow the user to set whether they want the notification on or off by default.