Some people like the ability to restrict a letterbox to a subset of members for various reasons. At this time, letterboxes may be restricted to other members with minimum P- or F-counts or to members of specific member groups. Someone can also restrict boxes so that only certain people can see the box (a "whitelist"). A dependency restricts a box (e.g., a bonus box) to only the users that have logged a find on a specific box (the dependency). The exact restrictions for a letterbox will not be displayed to help prevent abuse (for instance, some people may try to find a member who meets the requirements and bug them for the clue).

The specific reasons aren't important, and different people will have different reasons for the restrictions. Some people might restrict boxes to help ensure that search engines can't index them. Others might be wary that someone is targeting their boxes for vandalism. Other boxes might not be appropriate for everyone (perhaps it has an adult-oriented stamp) so the planter might want to ensure only specific people or types of people will look for it. It doesn't really matter what the reason is - a restricted box just means you have to meet the restrictions before you can access the clue on Atlas Quest.

If you find a box that is restricted, you won't be able to record finds on it or even find the listing on the Atlas Quest. For all intents and purposes, until you meet the restrictions, it's as if the box isn't listed on Atlas Quest at all. You can record the box as a find on an unlisted box if you are a premium member or wait until the box does show up in your searches once the restrictions are met. Most of the time, the restrictions are quite low. Most restricted boxes require less than ten finds and one plant.