SPF

SPF: Sender Policy Framework

About

SPF (Sender Policy Framework) is an anti-spam protocol in which a DNS record specifies what IP addresses are allowed to send messages with a "from" address coming from that domain. The IP addresses may be specified literally (numerically) or given as domain-names. SPF is defined in RFC 7208 (status).

DNS Configuration

Discussion of the DNS record format is in Section 3. SPF uses TXT records; there must be only one SPF record per domain or subdomain. A record's contents must start with "v=spf1" in order to be recognized as an SPF record.

The remainder of the contents consists of a mix of mechanisms and modifiers, combined according to these nearly-indecipherable rules:

  terms            = *( 1*SP ( directive / modifier ) )

  directive        = [ qualifier ] mechanism
  qualifier        = "+" / "-" / "?" / "~"
  mechanism        = ( all / include / a / mx / ptr / ip4 / ip6 / exists )
  modifier         = redirect / explanation / unknown-modifier
  unknown-modifier = name "=" macro-string
                     ; where name is not any known modifier

  name             = ALPHA *( ALPHA / DIGIT / "-" / "_" / "." )

Links

• Wikipedia
• RFC 7208 (status)