Re: Message-ID with IPv6 domain-literal

[Rupert Gallagher <ru...@protonmail.com>]

-------- Original Message --------
On Sep 24, 2021, 18:30, Grant Taylor < gtaylor@tnetconsulting.net> wrote:

On 9/24/21 10:17 AM, Rupert Gallagher wrote:
>> The RFC 5322 as cited is concerned about domains and their internet
>> address, where the sender's address needs to be resolvable through DNS
>> by the recipient.

>"where the sender's address" seems to be discussing the email address,
>which is completely independent from the Message-ID.

Nope.

The Message-ID is generated by the MUA, whose only reference is the sender's address. Bad MUA's use the LAN hostname of the sending machine, and thus generate non-RFC compliant headers. If the MUA does not include the Message-ID, then the server intervenes by adding its own RFC-compliant header, explicitly marked as added by server. Note that if the aim with the RFC's new nasty grammar for this limited to the uniqueness of the ID without any reference to the domain, then a random string [a-zA-z0-9]{N} would be enough if N is a big enough integer. But no, the RFC's grammar is at pains with domains and domain literals, so they are important and must have a semantics.

>"needs to be resolvable through DNS by the recipient" seems to be discussing the recipient's email system's ability to resolve something, which can include B2B partners across any intermediate network, be it a VPN or the public Internet. It also seems to mean that it doesn't matter if other DNS servers are able to resolve it or not.

All domains and domain literals in the headers are required to be resolvable. B2B make no exception to the rule. On VPN, being private networks by definition, they belong to the LAN-like network treatment: they are not public, and thus private for anyone outside those private network, both by RFC and by law (GDPR).

>> If the email infrastructure serves local messages in a company, then LAN addresses get the job done. But delivering messages across autonomous systems calls for *public* fully qualified domain names and their *public* IP addresses, or the delivery will fail.

> Again, email addresses and IP addresses are independent of the content of the Message-ID.

I disagree.

> You may dislike the content of the Message-ID. That's fine. That's your prerogative to have. But your prerogative does not negate the fact that the email was successfully delivered using a Message-ID that you
question.

Those e-mails are systematically rejected by our servers.

> The simple fact that the message arrived at your MTA such that SpamAssassin could score based on the questionable Message-ID is evidence to the fact that the message was successfully delivered.

They arrive in a special mailbox for admin verification, like a spam log. The end users do not see them at all.

RG