It could also be that the member has someone on ignore, so that member trying to send a message won’t get the pm option. To test this, one can try posting in a thread started by the intended recipient. If no option to do it you’ll see a message why.
You could post directly to them in the thread they posted in. Or use the visitor message if not too private, as other members can see visitor messages. This is separate from the pm system. I think you can also set it to just receive pm’s from your contacts or friends list.
Personally I just use the pm system if I don’t want to post something publicly. I too have gotten a few creepy messages but nothing bad enough to block, not yet anyway.
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Posted directly on site using iPhone