Never heard of Blue Sky; I don't believe we have a policy regarding Mastodon or that one, so we'll have to see how the links work out. X was banned because people were just posting links to items on that site rather than actually posting comments on TP, and it was becoming both nastily political and a tedious annoyance that people had to go into the X site to read what they were on about. If that can be avoided, and the links are really necessary, we might be able to tolerate them. The point being that if you have something to say, say it on TP and only refer to the SM site to back up your comments or illustrate them.