There are two categories for the message boards. The one where you post 7 to get 21 points at 3 points a piece liked you mentioned. There also is a bonus category at the very bottom of the my spark points page. For every 100 message posts you get 10 points.
So people use these message boards to post a bunch of messages to reach 100 posts.
Every day is a new beginning. Take a deep breath and start again!
I don't understand why so many of these say 10 points, since each post is for 3 points and we're trying to get 21 points. But here is my 1 post for 3 points! If someone will post and explain, I'd appreciate it.