This module (authres) is designed to provide support for RFC 5451/7001,
originally https://tools.ietf.org/html/rfc5451 (and then
https://tools.ietf.org/html/rfc7001 and https://tools.ietf.org/html/rfc7601) and
currently https://tools.ietf.org/html/rfc8601, 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)
- RFC 7281 Authentication-Results Registration for S/MIME
- RFC 7293, The Require-Recipient-Valid-Since Header Field and SMTP Service
  Extension, header field types
- RFC 7489 Domain-based Message Authentication, Reporting, and Conformance
  (DMARC)
- RFC 8617 The Authenticated Received Chain (ARC) Protocol
