Per user/admin filtering of individual/group emails
FreeMe is a lightweight e-mail filtering and reorganization tool for reducing clutter and highlighting messages of interest. It is intended to allow multiple administrators to specify individual rules for handling root e-mails, but can also be used in single-user mode.
Whitelight is a lightweight whitelist implementation built atop
procmail, with an autoresponder-based confirmation mechanism. Email with bogus return addresses (read: spam) is silently but effectively filtered out.