SPF

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SPF (RFC 7208) says which IP addresses may send mail for a domain. It needs the IP of the client that connected, so it is for SMTP servers.

result = MailAuth.SPF.check({192, 0, 2, 1}, "sender@example.com", "mx.example.com")
result.result     # :pass, :fail, :softfail, :neutral, :none, :temperror or :permerror
result.mechanism  # the term that decided it, such as "-all"
result.trace      # each record evaluated, through include and redirect

An empty MAIL FROM (a bounce) checks the HELO name as postmaster@<helo>.

All mechanisms, modifiers and macros of RFC 7208 are supported. The limits of section 4.6.4 apply: 10 terms that cause DNS lookups, 2 lookups that find nothing, 10 MX or PTR names. The library passes the RFC 7208 test suite.

ptr works, with the warning :ptr_used, since the RFC asks domains not to use it.

Mail read later

Mail read over IMAP has no trustworthy client IP. The Received: headers are written by whoever sent the message, so MailAuth does not read them. Without :ip, MailAuth.authenticate/2 gives SPF :none, reason :no_client_ip, and DMARC relies on DKIM.

Received-SPF

MailAuth.SPF.received_spf(result, receiver: "mx.example.org")