If you post a message in one of the subject areas of the forum all users will see it. If you want to send a message that only named recipients can see then you need to create a Private Message (a bit like an email) and choose their member names in the 'To:' field.
Once you have logged in, you can get to the Private Message area by clicking on the 'User Control Panel' option near the top left of the screen, then selecting the 'Private messages' tab.
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