This module (authres) is designed to provide support for RFC 5451/7001, originally http://tools.ietf.org/html/rfc5451 and currently http://tools.ietf.org/html/rfc7001 processing in Python. It also supports Authentication Results extensions: RFC 5617 DKIM/ADSP RFC 6008 DKIM signature identification (header.b) RFC 6212 Vouch By Reference (VBR) RFC 6577 Sender Policy Framework (SPF) draft-kucherawy-dmarc-base DMARC RFC 7281 Authentication-Results Registration for S/MIME RFC 7293, The Require-Recipient-Valid-Since Header Field and SMTP Service Extension, header field types SPF authentication results can relate to either the HELO identity or the Mail From. When creating header fields with SPF results, only set the identity used to evaluate the SPF result that's reported. You can use multiple objects to report both in a single header field. See the example in the tests file.