This is interesting. At some point, I think it'll be desirable to give increasing positive weight to emails with the DPF/DKIM/DMARC trifecta configured, since those are least likely to be problem emails (spam or phishing), but I wonder what the best avenue is to actually make that the default. It's almost certainly not this kind of unannounced cutoff.

Email is, I think, among the most distributed popular online services, and there's a ton of stuff that's legacy, self-managed, or otherwise janky. Supporting SPF, DKIM, and DMARC does put a burden on independent operators, but is it an undue or unreasonable one in the current landscape? Or is it just the new cost of doing business?

It seems like 90% of the spam I receive (on my google account) is sent from google addresses, so it will have valid SPF/DKIM/DMARC setup.

That said checking for these things is a good idea, the only problem I see is dropping the mail on the floor, rather than rejecting it at SMTP time - at least that lets the self-hosting users who haven't got things configured know their email is being rejected, and to pick up the phone instead.

There's nothing worse than sending an email, it being accepted, and then later discarded with no clue to either sender or recipient.

> but is it an undue or unreasonable one in the current landscape

Yes. In the first place, this should not even be a thing. Two corporations should not be in control of who can send e-mail. If they want to mark not having DMARC as spam, mark it as spam, or better yet flag it with a specific warning about the domain, but these games with refusing to deliver are just bullshit and essentially force a monopoly where other e-mail providers cannot compete because their e-mails aren't delivered.

None of them are a good 'Is this spam?' heuristic, though. All they do is ensure the sending domain isn't forged, but most spam, even phishing emails, doesn't really rely on that. Spammers are much more motivated than average to jump through the hoops necessary to set it up, as well. Any anti-spam signal needs to be much more expensive for spammers than regular senders.

Most spam I get is from Google, Microsoft and Amazon. We should pressure those to start dealing with the problem. Right now they are conveniently ignoring it.

> I wonder what the best avenue is to actually make that the default. It's almost certainly not this kind of unannounced cutoff.

En contraire, I think not delivering mail is the fastest way to adoption. People will use an old system for as long as it works. It now does not anymore.

I could be naive, but I don't see how this would be any more unreasonable than requiring HTTPS

There's no burden whatsoever. It's a one time setup that takes like 15 minutes.