if your message that you have sent does not appear in the sent box does it mean he has blocked me. thanks for your help.

Apparently so if you are to believe what the other people said in the other thread about this.

I wouldnt know....no one messages me haha :b

Not always.
It happens when somebody deletes your message from their inbox too. Some people like to empty their messages after they've read them, they might even have read and kept messages in their e-mail notifications and don't need to keep the one's on site for reference.
I've still had messages from people who've deleted my replies.
It happens when people leave the site if they close their account.... like they never existed
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