Sender ID - Standardization Issues

Standardization Issues

The pra has the disadvantage that forwarders and mailing lists can only support it by modifying the mail header, e.g. insert a Sender or Resent-Sender. The latter violates RFC 2822 and can be incompatible with RFC 822.

With SPF, mailing lists continue to work as is. Forwarders wishing to support SPF only need to modify SMTP MAIL FROM and RCPT TO, not the mail. That's no new concept; with the original RFC 821 SMTP forwarders always added their host name to the reverse path in the MAIL FROM.

The most problematic point in the core Sender ID specification is its recommendation to interpret v=spf1 policies like spf2.0/mfrom,pra instead of spf2.0/mfrom.

This was never intended by all published SPF drafts since 2003, and for an unknown large number of v=spf1 policies an evaluation for pra could cause bogus results for many cases where pra and mfrom are different.

This technical problem — in fact only four characters ,pra in the core Sender ID specification — was the base of an appeal to the Internet Architecture Board (IAB). In response to another prior appeal the IESG already noted that Sender ID cannot advance on the IETF standards track without addressing the incompatibility with a MUST in RFC 2822.