The VIP mailbox in Apple’s Mail program should show messages from contacts that you flag as VIP; however, there are instances where messages from your designated VIPs will not show up, leaving this feature somewhat unreliable. This may happen after upgrading or updating OS X to anew version, and if its happening then the fix should be relatively straightforward.

First, try rebuilding the VIP mailbox by selecting it in the Mail sidebar and then choose Rebuild from the bottom of the Mailbox menu.

Next, try re-sorting the VIP mailboxes. By default Mail will sort these mailboxes by the inbox they are in, but people experiencing this problem have found that re-sorting the mailboxes by “All Mailboxes” spurs mail to show messages properly:

1. Click the triangle to expand the VIP mailbox.
2. Select all of your VIP boxes by Shift-clicking or Command-Clicking them.
3. Choose Sort By > All Mailboxes from the View menu.

After doing this the mailboxes should sort properly, and you can then try changing their sort order to other values see if the mailboxes will maintain their messages, but if not then these should at least allow you to see the proper messages in the VIP folder.