How to block someone who is not on my Contact List? [1/1]

You can add him/her to your Block List. If you add someone to your Block List, you won't receive any more messages from him/her.
1.If you've just received a message from the person or if the person still appears in the Not In List group (on the bottom of your contact list), open a message window with the person and click the Block link.

Note: This option is only available in the message window when the message is from a user that is not on your contact list.

2.A warning message will be displayed after you click the link, explaining that the user will be added to your Block List. To confirm click YES.