spamd

spamd is the daemon component of SpamAssassin, an open-source system for filtering email and identifying spam. It runs as a background process and provides a network-accessible service that applies SpamAssassin's rules to incoming mail.

Clients such as spamc connect to spamd to request a spam assessment. The daemon accepts a message or headers, runs the built-in rule set (including Bayesian classifiers, rule-based tests, and reputation checks), and returns a verdict, a numeric score, and a concise report outlining which tests fired.

spamd is designed to handle multiple requests concurrently and can be configured to run with multiple worker processes. It integrates with mail transfer agents (MTAs) to filter mail in transit, commonly via local or network connections. It can apply user- or system-wide configurations and can be tuned through local configuration files to adjust sensitivity, whitelists, and blacklists.

Configuration and security considerations are important for spamd deployments. Administrators typically restrict access to trusted hosts, run the daemon under a limited user account, and employ containment measures such as chroot environments. Keeping the SpamAssassin rule set up to date and maintaining appropriate local rules help maintain effective filtering.

History and context: SpamAssassin and its spamd daemon appeared as widely used open-source tools for combating email spam in the early 2000s. spamd is the network-facing component that enables scalable, server-side filtering on mail systems, often in combination with MTAs and mail delivery pipelines.