Clement is a completely free and open source command-line/web-based software project implemented in C and designed from the offset to work as an e-mail server firewall, with the main purpose of trapping most of the unwanted messages (also known as spam) at the earliest possible stage, so they won’t reach your users’ inboxes.
Operates in two distinct modes
The application is engineered in such a way that it can operate in two distinct modes, either as a smart spam filtering device that transmits email messages to another SMTP (Simple Mail Transfer Protocol) server, or as a standard MTA (Mail Transfer Agent) that stores e-mail messages in the recipient's own area.
Supports popular Mail Transfer Agents
When working as Mail Transfer Agent, it is good to know that Clement supports popular MTAs, such as Sendmail, Exim, Postfix, Exchange, and many others. It filters e-mails while the SMTP session is still pending.
Designed for Red Hat Enterprise Linux
Clement is a software designed for the Red Hat Enterprise Linux (RHEL) operating system. It works, of course, with its open source derivatives, such as the popular CentOS and Scientific Linux distributions. It is compatible with both 32 and 64-bit flavors of the aforementioned distributions.
Detailed installation instructions are provided for all supported GNU/Linux OSes on the https://www-prod2.clemsafe.net//download.php?&lang=eng web page. A source RPM package is also available for download for those of you who want to inspect and hack Clement’s source code.