What happened when you clicked the link? Did it try to load a Java applet?
Also yes it's fake they message you via your inbox on Runescape for bans/mutes etc.
100% fake. What you can do, is in the email, right-click the link, click on "Copy Shortcut" paste that into word / notepad etc, and it will show you the link you were about to click on. It is fake, and it is a phising website.
Also, read the email fully. They made spelling mistakes, something Jagex wouldn't do.
Please guys, be really careful with sites that prompt you to run a java applet. These can be really dangerous.

