Untrusted posters list is the list of email addresses (no names) of posters whose posts should always be reviewed by mods, even if they are posting to a preapproved thread.

Example:

anonymous
nobody
remailer
mixmaster
losingtemper@aol.com
The above would ensure that all addresses containing substrings above would always come to human attention. A nice way to deal with anon remailers.