SPAM: Limit replies for non-followers.

In an effort to stop spam, a limit should be imposed on the number of replies that can be sent to people who are not followed by the recipient. Then spammers that I do not follow will send far less generic message that show in my replies feed for days - and cannot be deleted.

I think there should also be a limit to the number of mentions per tweet as many of my replies are like this:
"Thanks for RT. #followfriday @username1 @username2 @username3 @username4 @username5 @username6 @username7 @username8 @username9 @username10 @username11 @username12 @username13 @username14 @username15 @username16 @username17 @username18".

Great, someone noticed for a moment that I exist, but there is no content in a message like this. It would also put a stop to the overuse of the #followfriday hashtag which means nothing to me because so many users do it that they can't truly know that many people well enough to recommend them, and there is less to read due to lists of names in my Twitter stream, like the example tweet above.