senderid

SenderID is an email authentication framework developed by Microsoft in the early 2000s. It aims to determine if a message claiming to be from a given domain is sent by a host authorized to send mail for that domain. The approach extends the existing SPF concept by using the Purported Responsible Address (PRA)—the address in the message From header—as the domain for which an authorization policy is published.

To validate, a receiving MTA derives the PRA domain and performs a DNS check for an SPF-like policy associated with that domain. If the sending IP is authorized by the PRA domain's policy, the message passes the SenderID check; otherwise it fails or is treated as neutral. Implementations typically integrate with existing mail filtering and reputation systems.

History and status: SenderID was proposed in 2004–2005 and was not standardized by the IETF. It faced criticisms over PRA-based checks, spoofing vectors, and compatibility with mail forwarders. By the late 2000s, broad adoption waned, and DMARC, SPF, and DKIM became the prevailing approaches to email authentication. Today, SenderID is largely considered obsolete and is not widely implemented in modern mail systems.

Its limited adoption and the success of SPF, DKIM, and DMARC reflect a shift toward these mechanisms in contemporary email security practices.