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Anti-spam technique: Sender-ID
Date of first use: 2005
Effectiveness: Medium
Popularity: Low
Difficulty of implementation: Medium
Where implemented: MTA
Harm: Low

Sender-ID is a path management technique that assigns a set of permitted IP addresses to the domain in a message's From: or Sender: header, selected by a Purported Responsible Address (PRA) algorithm. The Sender-ID record is a TXT record published in the DNS under the name of the domain, in a complex format. If the IP address from which a message is sent matches the domain's record, Sender-ID succeeds. If not, there are various levels of hard and soft failure.

Sender-ID has its own TXT message format but will fall back to using SPF records.

Sender-ID is similar to SPF with similar advantages and disadvantages. Its primary user and proponent was Microsoft. The PRA algorithm in RFC 4407 is patented, which turned out to be an impediment to adoption, even though Microsoft offered a free public license.


  • RFC 4406
  • RFC 4407