If you can see ‘hidden messages’ in your Inbox, this is because the profile filters that you set have filtered out messages from people who don’t meet your criteria.
If this applies to you, you’ll see this message: ‘(number) messages are hidden by your filter settings. Do you want to show them all?’.
If you'd like to see the messages that have been filtered out, click ‘Show them all’. You can change your filter settings at any time by clicking on ‘Account’ and ‘Filtering’.