# 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](https://spamscanner.net/docs/how-it-works/#authentication)

Authenticated Received Chain: signatures that carry authentication results across forwarding servers.

## [ClamAV](https://spamscanner.net/docs/how-it-works/#attachments)

An open-source antivirus engine. Its daemon, clamd, scans files sent over a socket.

## [Content filter](https://spamscanner.net/docs/postfix/#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](https://spamscanner.net/docs/how-it-works/#authentication)

DomainKeys Identified Mail: a signature over a message, checked with a public key published in the sender's DNS.

## [DMARC](https://spamscanner.net/docs/how-it-works/#authentication)

A DNS policy telling receivers what to do when mail claiming a domain fails SPF and DKIM alignment.

## [DNSBL](https://spamscanner.net/docs/getting-started/#turn-on-more-checks)

DNS blocklist: a list of IP addresses (or domains, for a URIBL) known for spam, queried over DNS.

## [GTUBE](https://spamscanner.net/docs/postfix/#3-test-it)

Generic Test for Unsolicited Bulk Email: a fixed string every spam filter treats as spam, for testing.

## [Ham](https://spamscanner.net/docs/how-it-works/#the-classifier)

Wanted mail: the opposite of spam.

## [Lookalike domain](https://spamscanner.net/phishing-detection/)

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](https://spamscanner.net/docs/postfix/#milter)

Mail filter: a protocol from Sendmail, also used by Postfix, that lets a separate program inspect each message during the SMTP session.

## [MTA](https://spamscanner.net/docs/mail-servers/)

Mail transfer agent: the server software that sends and receives email, such as Postfix or Exim.

## [Ollama](https://spamscanner.net/docs/llm/#quick-start-with-ollama)

A program that downloads and runs open language models on your own machine, with an HTTP API.

## [Punycode](https://spamscanner.net/docs/how-it-works/#phishing)

The ASCII form of an internationalized domain name, starting with xn--.

## [Spam score](https://spamscanner.net/docs/scoring/)

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](https://spamscanner.net/docs/mail-servers/#a-drop-in-for-spamassassins-spamd)

SpamAssassin's daemon. Its protocol is spoken by spamc, Exim, Haraka and other SpamAssassin clients.

## [SPF](https://spamscanner.net/docs/how-it-works/#authentication)

Sender Policy Framework: a DNS record listing the servers allowed to send mail for a domain.

## [X-Spam headers](https://spamscanner.net/docs/postfix/)

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.