clamavmilter

clamavmilter, also known as clamav-milter, is a mail filter that integrates the ClamAV antivirus engine with mail transfer agents using the milter protocol. It is designed to scan messages and attachments for malware in real time as they pass through an MTA such as Sendmail, Postfix, or Exim.

The filter operates by running as a separate process or daemon and communicating with a running ClamAV daemon (clamd) to perform on-the-fly scanning. For each message, it forwards the content to clamd for virus scanning and then returns a Milter response to the MTA. Depending on configuration, a detected virus can cause the message to be rejected, temporarily failed, or marked with headers or notes rather than blocked. It can also be configured to block or mark messages rather than fully rejecting them.

Configuration is typically done through its own config file, where one can specify the clamd socket or host/port, timeouts, and the actions to take when a virus is found. It relies on the ClamAV signature database, which is kept up to date by the ClamAV update utility (freshclam).

As a Milter, clamavmilter integrates with MTAs that support milters, providing a modular approach to antivirus scanning. It is widely used in mail-filtering deployments and can be complemented with additional filtering rules or spam-checking systems.

See also: ClamAV, ClamAV Milter, Milter, Postfix, Sendmail, Exim.