So, you have a message area that's out of control, and you (or another user) are willing to review every post and delete or validate every message as appropriate.
Any message posted into a sub-board by a user who matches the “Moderated Posting User” ARS in the SCFG configuration for a sub-board will have their message marked with a “moderated” flag. When a user who is not the sub-op (sub-board operator) or the sysop is reading messages, they will be unable to view any messages posted or imported after the oldest moderated message until that message is either deleted or validated by a sub-op or sysop.
When a sub-op or sysop reads the messages, she is prompted to validate the message. If she declines to do so, she is prompted to delete the message. If she does neither, this leaves all messages posted after the unvalidated one unreadable by normal users (and not exported to message networks) and this may not be noticed by the sub-op.
If a sysop or sub-op sees the following message while reading a sub-board:
WARNING: You are reading messages past the last unvalidated message
This is an indicator that at least one older unvalidated message remains (and its message number is included in the warning) and is blocking the viewing or exporting of messages after it, including the message being viewed. A sysop or sub-op needs to take action (validate or delete the message mentioned in the warning message) to correct this situation.