pgl4rbl implements a Postfix policy server that mixes two widely used techniques: greylisting and RBL (DNS blacklists). The idea is that greylisting is applied only to SMTP clients that match a RBL; this means that normal clients are not delayed (such as with a normal greylisting implementation), and RBL false positives do not cause problems (like when outright blocking them at the SMTP level).
ChildProt is a child protection policy daemon for Postfix. It checks a list of recipient addresses. If the current recipient address is found, the sender address is verified against a whitelist. If the current sender address is found, the mail will be delivered to the recipient. If the sender address is not found on the whitelist, the mail will be redirected to a delegate of the recipient. If the recipient address is not found the mail will be delivered to the recipient too.
POP-Before-SMTP-Auth is a POP before SMTP daemon for Dovecot and Postfix that works by scanning mail server log files. The line-matching regex can be changed from the configuration file, in case Dovecot's logging format changes, and also to adapt the script for use with something besides Dovecot. Presently the script requires that the IP address appear on a single line with the successful login in the log file.
checkMX is a Perl daemon which monitors remote MX servers for a domain's overall health. If all the MX hosts are down and the domain can no longer receive mail, checkMX updates the Postfix relay_domains file so it will start accepting mail for the broken domain. Once the domain can start accepting mail on its own, checkmx will flush the mail queue for delivery and remove it from postfix relay_domains file. This prevents spammers from using the backup MX server as a spam vector.
Clement is an email server application. Its main function is to block unwanted mail (spam) as soon as possible in the email exchange process. It accepts or rejects email while the SMTP session, initiated by the email sender, is still pending, accepting legitimate email messages without the need to return an error status to non-existent or "borrowed" return address later. Clement can operate in two modes, either as a standard MTA (as sendmail, Postfix, Exim, Exchange, etc.) to store email in the recipient's own area, or to transmit the mail to an another SMTP server acting as smart spam filtering device. Each email domain name Clement knows about can be treated in one of these two modes depending on the group to which the domain name has been set. Each message is verified by a virus scanner (ClamAV) while the SMTP connection is still open, but the refusal of mail and the reason for refusal is notified to the actual sender. Mail management is done via a Web interface and can be delegated to three administrative levels (Root-Admin, Group-Admin, Domain-Admin). Standard users can access their own logs (sent email status, email rejected, quarantined email, etc.). With this interface, the user can handle the rejection and acceptance of mail. Users who are level "Admin" can access the session logs (via the Web interface). Clement uses a SQL database (PostgreSQL, MySQL) to store and manage logs, user profiles, and dynamic management of directives concerning the sender-receiver relationship.