This will be in a future release. A piece of this is already in 3.0. Each board and user has a security level. In a future version you will be able to change these. Users with a security level equal or greater than the board's security level will be able to see the boards and post on them if they are not set to read only. Users with a security level lower than the board's security level will not even be able to see the boards.
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'If it's worth doing, It's worth doing loudly'
Scream
