You need to be friends with someone in order for them to be notified of your private messages. Otherwise, your message will be delivered but they may not be aware of it, as it’s stored in a spam section.

If you don’t get a reply in a reasonable time, you may notify those users by posting on their X-Stream, or mentioning them in a post (use @ before their username).

Note: moderators and thriXXX team members can still receive your messages without being in your friend list.