Port 783
SpamAssassin spamd
SpamAssassin's spamd daemon listens on port 783 to perform content-based email filtering, identifying spam through a vast array of heuristic and signature-based tests. Designed to work alongside mail transfer agents, spamd enables rapid analysis of inbound mail streams, efficiently tagging or rejecting unwanted messages. It is a popular tool integrated into many email security solutions to reduce spam volume and protect users from unsolicited messages and common email threats..
Technical Details
SpamAssassin’s spamd is a lightweight, daemonized server component of the Apache SpamAssassin project. It listens on port 783, typically over TCP, providing a fast network-based API to analyze email content for spam characteristics. Rather than invoking SpamAssassin’s full Perl process per message, spamd optimizes system performance by maintaining a persistent service, greatly reducing resource utilization.
The communication primarily follows the spamc/spamd protocol, enabling email systems to submit mail messages for scoring. The client, spamc, connects via TCP port 783 and streams mail content; spamd then evaluates the content against a wide array of rules, Bayesian filters, and network-based tests (like RBLs and URL reputation). The results include a spam score and optional modification of message headers with spam-related metadata.
While it typically runs on email gateways or mail servers, spamd can be configured for local or distributed deployments, scaling from single-server installations to complex, clustered environments. Port 783’s role is thus crucial in enabling fast, asynchronous filtering operations within the broader email infrastructure.