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
History and status: SenderID was proposed in 2004–2005 and was not standardized by the IETF. It faced
Its limited adoption and the success of SPF, DKIM, and DMARC reflect a shift toward these mechanisms