Email spam filter glossary
Short definitions of the email and spam filter terms used in the Spam Scanner documentation. Each term links to the page that explains it.
- ARC
- Authenticated Received Chain: signatures that carry authentication results across forwarding servers.
- ClamAV
- An open-source antivirus engine. Its daemon, clamd, scans files sent over a socket.
- Content filter
- A program a mail server hands each accepted message to, which passes it back with headers added. Postfix runs Spam Scanner this way with spamscanner filter.
- DKIM
- DomainKeys Identified Mail: a signature over a message, checked with a public key published in the sender's DNS.
- DMARC
- A DNS policy telling receivers what to do when mail claiming a domain fails SPF and DKIM alignment.
- DNSBL
- DNS blocklist: a list of IP addresses (or domains, for a URIBL) known for spam, queried over DNS.
- GTUBE
- Generic Test for Unsolicited Bulk Email: a fixed string every spam filter treats as spam, for testing.
- Ham
- Wanted mail: the opposite of spam.
- Lookalike domain
- A domain that imitates another with swapped characters or letters from another alphabet, such as paypa1.com, or pаypal.com with a Cyrillic а.
- Milter
- Mail filter: a protocol from Sendmail, also used by Postfix, that lets a separate program inspect each message during the SMTP session.
- MTA
- Mail transfer agent: the server software that sends and receives email, such as Postfix or Exim.
- Ollama
- A program that downloads and runs open language models on your own machine, with an HTTP API.
- Punycode
- The ASCII form of an internationalized domain name, starting with xn--.
- Spam score
- The sum of the points of every test that fired. Spam Scanner marks a message as spam at 5 points and tells a mail server to refuse it at 15.
- spamd
- SpamAssassin's daemon. Its protocol is spoken by spamc, Exim, Haraka and other SpamAssassin clients.
- SPF
- Sender Policy Framework: a DNS record listing the servers allowed to send mail for a domain.
- X-Spam headers
- Headers such as X-Spam-Flag, X-Spam-Score and X-Spam-Status that a spam filter adds to a message, so mail programs and Sieve rules can sort it.