What is Maintenance Mode?
The ProBoards "Maintenance Mode" feature switches your forum into a staff-only access mode. In Maintenance Mode, only members of your forum that are staff members are able to login and access your forum. All other members and guests will be locked out of the forum until Maintenance Mode is disabled.
You can enable Maintenance Mode by visiting your forum's Administration Area, clicking on "General Settings" under the "Customize Your Forum" section, and changing "Maintenance Mode" to "Yes."