> "I don't want to" is not a valid excuse

for the client. If you're implementing a server, "the client SHOULD but didn't" isn't a valid excuse to reject a client either.

You can do it anyway, you might even have good reasons for it, but then you sure don't get to point at the RFC and call the client broken.

▲ geocar 6 hours ago | parent | next [-]

> isn't a valid excuse to reject a client either.

Yes it absolutely is: https://www.rfc-editor.org/rfc/rfc2119 is quite clear.

    3. SHOULD   This word, or the adjective "RECOMMENDED", mean that there
       may exist valid reasons in particular circumstances to ignore a
       particular item, but the full implications must be understood and
       carefully weighed before choosing a different course.

If the client SHOULD do something and doesn't, and your server does not know why, you SHOULD disconnect and move on.

If the server has considered fully the implications of not having a Message-ID header, then it MAY continue processing.

In general, you will find most of the Internet specifications are labelled MUST if they are required for the protocol's own state-processing (i.e. as documented), while specifications are labelled SHOULD if they are required for application state-processing in some circumstances (i.e. other users of the protocol).

▲ Dylan16807 3 hours ago | parent | next [-]

> If the client SHOULD do something and doesn't, and your server does not know why, you SHOULD disconnect and move on.

That is not a rule.

In this situation the server can reject any message if it wants to, and not doing a SHOULD tests the server's patience, but it's still ultimately in the "server wanted to" category, not the "RFC was violated" category.

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geocar 2 hours ago | parent [-]

You are confused.

The RFC is a request for comments. The specific one in question is about Internet Mail.

If server implementers want their mail to be delivered these are things they SHOULD do.

That's it.

It isn't something you can give to your lawyer, and nobody cares about your opinion about what you think "should" means you can make someone else do. This is how it is.

	▲	Dylan16807 an hour ago \| parent [-]
		You are confused about what I'm doing. I'm not telling anyone what to do. I'm saying what category their actions fall into. And the line of yours I quoted is still not supported by anything.

▲ drecked 3 hours ago | parent | prev | next [-]

That clearly means it’s not required.

How does Google know whether or not the sender has a valid reason? They cannot know that so for them to reject an email for it means they would reject emails that have valid reasons as well.

	▲	conductr 2 hours ago \| parent \| next [-]
		How would the sender know the consequences of sending without the header? You shouldn’t assume anything here. As a sender, you should include it unless you’ve already worked out what the recipient is expecting or how it will be handled. Doing this with email is silly because the client is sennding to so many different servers they know nothing about so it’s basically a requirement to include it.
	▲	geocar 3 hours ago \| parent \| prev [-]
		> That clearly means it’s not required. You and I have different definitions of "clearly" It is not required for the protocol of one SMTP client sending one message to one SMTP server, but it is required for many Internet Mail applications to function properly. This one for example, is where if you want to send an email to some sites, you are going to need a Message-ID, so you SHOULD add one if you're the originating mail site. > How does Google know whether or not the sender has a valid reason? If the Sender has a valid reason, they would have responded to the RFC (Request For Comments) telling implementers what they SHOULD do, rather than do their own thing and hope for the best! Google knows the meaning of the word SHOULD. > it means they would reject emails that have valid reasons as well. No shit! They reject spam for example. And there's more than a few RFC's about that. Here's one about spam that specifically talks about using Message-ID: https://datatracker.ietf.org/doc/html/rfc2635

▲ buran77 3 hours ago | parent | prev | next [-]

> If the server has considered fully the implications

The server "considers" nothing. The considerations are for the human implementers to make when building their software. And they can never presume to know why the software on the other side is working a certain way. Only that the RFC didn't make something mandatory.

The rejection isn't to be compliant with the RFC, it's a choice made by the server implementers.

▲ hsbauauvhabzb 5 hours ago | parent | prev [-]

Either the server must explicitly confirm to servers or the clients must accept everything. Otherwise message delivery is not guaranteed. In the context of an email protocol, this often is a silent failure which causes real-world problems.

I don’t care what the protocol rfc says, the client arbitrarily rejecting an email from the server for some missing unimportant header (for deduction detection?) is silly.

▲ behringer 4 hours ago | parent [-]

If it was unimportant it would be MAY.

▲ hsbauauvhabzb 3 hours ago | parent [-]

Is the server somehow unable to inject an ID if the sender did not send one? Stop hiding behind policy and think for yourself.

	▲	geocar 2 hours ago \| parent [-]
		> Is the server somehow unable to inject an ID if the sender did not send one? Yes. https://www.rfc-editor.org/rfc/rfc2821#section-6.3 refers to servers that do this and says very clearly: `These changes MUST NOT be applied by an SMTP server that provides an intermediate relay function.` That's Google in this situation. > Stop hiding behind policy and think for yourself. Sometimes you should think for yourself, but sometimes, and friend let me tell you this is one of those times, you should take some time to read all of the things that other people have thought about a subject, especially when that subject is as big and old as email. There is no good reason viva couldn't make a Message-ID, but there's a good reason to believe they can't handle delivery status notifications, and if they can't do that, they are causing bigger problems than just this.

▲ Veserv 6 hours ago | parent | prev | next [-]

You are describing MAY.

“MAY This word, or the adjective "OPTIONAL", mean that an item is truly optional… An implementation which does not include a particular option MUST be prepared to interoperate with another implementation which does include the option, though perhaps with reduced functionality. In the same vein an implementation which does include a particular option MUST be prepared to interoperate with another implementation which does not include the option (except, of course, for the feature the option provides.)”

Note how it explicitly calls out interoperation with implementations that do or do not implement MAY. As a exception that proves the rule, we can reasonably assume that not interoperating with a system ignoring a SHOULD rule is a correct implementation and it is the fault of whoever is not implementing SHOULD.

▲ Arnt 7 hours ago | parent | prev [-]

Hearsay has it that the reason is spam. Spam messages are said to have massively higher chances of minor RFC violations when they arrive at the destination server.

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shadowgovt 6 hours ago | parent [-]

Most of the time, in my experience, when one encounters a situation like this in Internet tech (i.e. "why is this suggestion treated like a hard requirement?"), this is the answer: "because attackers found a way to exploit the lack of the suggestion's implementation in the wild, so it is now a hard requirement."

The standards, to my observation, tend to lag the CVEs.

Side-note: If someone has built a reverse-database that annotates RFCs with overriding CVEs that have invalidated or rendered harmful part of the spec, I'd love to put that in my toolbox. It'd be nice-to-have in the extreme if it hasn't been created yet.

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atherton94027 6 hours ago | parent [-]

How is not having a message-id a security risk? It seems that Gmail is being pedantic for no reason

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geocar 6 hours ago | parent | next [-]

> How is not having a message-id a security risk?

CVE classify a lot of things that have nothing to do with security.

Not having a Message-ID can cause problems for loop-detection (especially on busy netnews and mailing lists), and with reliable delivery status notification.

Dealing with these things for clients who can't read the RFC wastes memory and time which can potentially deny legitimate users access to services

> It seems that Gmail is being pedantic for no reason

Now you know that feeling is just ignorance.

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hsbauauvhabzb 5 hours ago | parent [-]

So add a message id at the first stop, or hard ban the sender server version until they confirm. A midway point that involves a doom switch is not a good option.

	▲	geocar 3 hours ago \| parent [-]
		> So add a message id at the first stop That should have already happened. Google is not the "first stop". > hard ban the sender server version until they confirm SMTP clients do not announce their version. Also I don't work for you, stop telling me what to do. > A midway point that involves a doom switch is not a good option. No shit. That's almost certainly a big part of why Google blocks messages from being transited without a Message-ID.

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shadowgovt 3 hours ago | parent | prev [-]

Because in practice it showed up for a period of time as a common thing in spam-senders. They were trying to maximize throughput and minimize software maintenance costs, so they leave out things that the spec says are optional. But that makes "a commonly-implemented optional thing was left out" into a stronger spam signal.

Is it still a strong spam signal? Hard to say. Sources disagree. But as with laws, heuristics, once added, are often sticky.