Re: [dmarc-ietf] Errors in RFC 8601, was Question about changes introduced by erratum

Damian Lukowski <> Sun, 22 March 2020 19:33 UTC

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To: John Levine <>,
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From: Damian Lukowski <>
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Date: Sun, 22 Mar 2020 20:34:11 +0100
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Subject: Re: [dmarc-ietf] Errors in RFC 8601, was Question about changes introduced by erratum
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> RFC8601 sec 2.7.2 refers to RFC 7208 for "mailfrom".  RFC 7208 sec 1.1.3
> says that the MAIL FROM, which I whink we can assume is the same thing,
> is the RFC5321.MailFrom from RFC 5598.  RFC 5598 says that's a mailbox,
> not a domain name.

Those definitions are too confusing for me. RFC5598 says

> RFC5321.MailFrom is the address in the SMTP "Mail From" command

So is RFC5321.MailFrom the Reverse-Path from RFC5321, or only the
Mailbox part of a Reverse-Path? I would expect it to be the full
Reverse-path, because

> RFC5321.Return-Path:  Set by - Originator
>  The MDA records the RFC5321.MailFrom address into the
>  RFC5321.Return-Path field.

and a Return-Path field usually contains "<" ... ">", so it cannot be a
plain Mailbox.

But then the term "MAIL FROM" in
>    As such, throughout this document the term "MAIL FROM" will be used,
>    which is defined as the RFC5321.MailFrom (reverse-path) identity
>    described in [RFC5598].

cannot be identical to RFC5321.MailFrom, because if it were, we would
have smtp.mailfrom = "MAIL FROM" = RFC5321.MailFrom = "<" ... ">",
which is not given by the examples.

Another possibility to interpret the quote is that one obtains the "MAIL
FROM" by picking "the" identity out of the RFC5321.MailFrom. But there
are two sensible identities defined in RFC5598 that one could pick: The
mailbox or the domain name.

> The forms of identity used by Internet Mail are: mailbox, domain
> name, [...]

By the way, an RFC5321 mailbox allows address-literals which are not
covered by the right hand side of RFC8601's pvalue, and one cannot use
the left hand side because of

> If the value portion of a "pvalue" construction identifies something
> intended to be an email identity, then it MUST use the right-hand
> portion of that ABNF definition.