[bcrl]

Sadly the article doesn't really touch on whether or not DMARC accomplishes anything truly useful. When I enabled DMARC for ingress email on one of my own mail servers, it ultimately ended up regularly blocking a handful emails from customers, yet virtually all the spam coming in had valid SPF / DKIM / DMARC, as do most of the phishing attacks.

The core problem is that the real need of email end users need is a way of determining whether or not to trust a given sender. Signatures are purely a technical measure which provides no information on the trustworthiness of the sender. The end result is that email scoring still has to be content based, and the signature check technologies are pure noise with no useful signal for the purpose of determining if an email should actually show up in my inbox.

The tech industry has a bad habit of providing solutions to problems adjacent to problems the user actually needs solved while leaving the user's actual problem unresolved.

[bawolff]

> The core problem is that the real need of email end users need is a way of determining whether or not to trust a given sender.

Which is only the core problem because dmarc fixed the other core problem of figuring out who the given sender is.

DMARC does not solve everything, but it does make other solutions more effective.

[deknos]

> Which is only the core problem because dmarc fixed the other core problem of figuring out who the given sender is.

Does it verify the sender or the domain/service which the sender is using?

[brightball]

> virtually all the spam coming in had valid SPF / DKIM / DMARC, as do most of the phishing attacks.

This should create a means to go after the domain owners via registrar and trail of ownership, even so far as blocking email from the domain.

Forcing the spammers to pass DMARC creates a burden and an evidence trail that didn't exist before.

[WorldMaker]

Can we use DMARC to ask Gmail to close registrations? Google Calendar to allow far fewer people the ability to send invite notifications? Firebase to close registrations? Azure? Microsoft 365? AWS SES?

It feels like the biggest spammers have swung back to just abusing SaaS and getting SPF / DKIM / DMARC for free from one of the big email providers.

[bcrl]

Exactly this. Spammers have the technical competence to overcome any technical hurdle, so using evidence of technical competence achieves nothing.

If it were possible to charge $0.25/email for delivery, I'd be more than happy . However, I'm sure large tech firms will need to say that is "too hard to implement at scale".

[WorldMaker]

Stamp costs don't stop snail mail spam, either, unfortunately. I would be concerned if we added something like bitcoin fees to email delivery rather than curtail spam it would just further encourage grifters seeking ROI on their spam deliveries.

[ebcode]

What if a single email cost $0.001 cent to send, and it was paid to the recipient? For $10, you could send 10,000 emails. For recipients, every 1,000 emails they get is a dollar in their wallet. You’d need something like a blockchain for this to work because the traditional payment processors still haven’t figured out micropayments.

[locknitpicker]

> What if a single email cost $0.001 cent to send, and it was paid to the recipient? For $10, you could send 10,000 emails. For recipients, every 1,000 emails they get is a dollar in their wallet.

I'm not sure you realize your proposal's only contribution is to worsen spam. You are unwittingly creating an incentive for email providers to lift anti-abuse filters and to maximize the volume of spam delivered to you.

[wahern]

If snail mail cost $0.001 per recipient people would be getting much, much more junkmail. Likewise, if e-mail cost as much as even bulk snail mail, there'd be much less spam.

Some sort of payment scheme is really the best, most durable option. The problem of mailing-lists and personal correspondence could be solved by an exclusion mechanism where the recipient effectively whitelists senders, explicitly or implicitly (e.g. whitelist a replying-sender automatically if a recipient initiates a conversation).

[locknitpicker]

> If it were possible to charge $0.25/email for delivery, I'd be more than happy .

I'm baffled by this blend of replies. What exactly do you believe charging for an email would do? I mean, other than fabricating a revenue stream. Do you seriously believe that spam would vanish as soon as anyone charged for it's delivery? Because advertisers already pay for reaching their target audiences, and do so well beyond email.

[illliillll]

What spammers are using the same domain for longer than couple of hours?

What do you expect to achieve by blocking an already abandoned domain?

[acdha]

@gmail.com and @outlook.com are like 90% of the spam I receive. What’s missing is effective accountability for those two companies hosting persistent spam groups who operate for months unimpeded.

[bigbuppo]

They're generally hosted on a google or microsoft 365 or something slightly less shady. Good luck with that.

[thedougd]

The primary purpose of DMARC is to prevent impersonation not to prevent spam. I own a domain, I implement DMARC to make sure others know when email from my domain is legitimately from my domain.

[bcrl]

Then you don't deal with email in the real world. DMARC prevents legitimate emails from people in the real world from being delivered because people make mistakes with their email systems. Passing DMARC is not a signal that the email isn't legitimate; it's merely a sign that someone correctly set up their mail server to modern standards. The email might be an impersonation, or not. There's no way to know.

DMARC does absolutely nothing to prevent the kind of impersonation that occurs in the real world. It doesn't block homoglyphs or or typo-squatting or all the other forms impersonation that matter. It has failed at preventing impersonation.

Just a few days ago I had a phishing email from an elderly woman I had previously done some work for. The message passed DMARC and everything else, and the domain it was sent from was valid. But it was not legitimate; it was an impersonation of her which became obvious once the content was read.

DMARC is noise, not signal. It has to be ignored in the real world as it provides virtually no value beyond blocking emails pretty randomly because someone made a mistake when rotating their DKIM keys or one of a million other mistakes that do happen.

[thedougd]

Okay but that doesn’t detract from the intended purpose of DMARC.

[ryandrake]

Perfect example of "The Purpose Of A System Is What It Does."[1]

1: https://en.wikipedia.org/wiki/The_purpose_of_a_system_is_wha...

[bigstrat2003]

That saying is bullshit. The purpose of a system is, by definition, what it is intended to do, not what it does. You can judge efficacy by the results, but not the purpose.

[HenriTEL]

Isn't that the purpose of DKIM and SPF already?

[wafflebot]

DKIM and SPF validate a message. DMARC sets a policy as to what to do with it (quarantine/reject.)

[warkdarrior]

ELI5: https://www.reddit.com/r/sysadmin/comments/16gvtdj/comment/k...

[joemi]

Wish I didn't have to log in to reddit to read that post. RIP useful reddit links.

edit: looks like I had an extension that was redirecting to old.reddit.com, and it was old reddit that required login. Though when I turned that extension off, I got a "blocked by reddit security" error. ugggh.

[daneel_w]

Yes and no. DKIM signs part of the envelope to help recipients detect alteration (by verifying authenticity), SPF locks down the permissible origins for the sender. SPF is in itself imperfect and can in some situations be exploited on open-access shared systems. If the two are used in concert they offer decent protection.

[kbolino]

Using both has to be done very carefully, because a positive result from the weaker one (SPF) will override a negative result from the stronger one (DKIM). You should maximally use DKIM and minimally use SPF. Ideally, you should not use SPF at all, but there are some senders that still don't support DKIM.

[zahrc]

Many email providers and third party security tools default settings automatically bounce or block SPF failures, no matter what DKIM says... so no, not using SPF completely is a bad idea.

Using it minimally is correct, thou. Route outbound mail through as few controlled relays as possible so your SPF record only needs to list infrastructure you actually *own*, rather than growing it every time a new tool needs to send mail.

I have seen way too many clients almost hit the char limit in a TXT record

[kbolino]

SPF failures overriding DKIM successes is a direct violation of RFC 7489 section 4.2 [1]. I have never observed such behavior in the wild, though my experience may be more limited than yours. There are two possible explanations anyway, one is that the DMARC record was missing or misconfigured, the other is that the DKIM check did not actually succeed even though you had reason to believe it should have (e.g., misaligned sender domain, invalid/stale/rotated key, etc.).

I would certainly agree that DKIM is harder to get right. However, the TXT record data size limit is surmountable. You can either use EC algorithms, which have much shorter keys, or stick with e.g. RSA and its very long keys, but span them across multiple 255-byte record data chunks. That having been said, I still think DNS providers should do more to make configuring DKIM easier.

Ultimately, if you have SPF and DKIM set up such that both cover all senders, then you are just using SPF. It is the simpler and more forgiving mechanism, so its broad-scoped successes will always swallow DKIM in practice. The only reason I can think of to do this anyway is if you suspect your email provider will change IPs on you and they don't provide their own SPF record, but if that were the case, they are basically telling you not to use SPF in the first place.

EDIT: RFC 7489 was superseded by RFCs 9989-9901 rather recently. Nevertheless, the definition of success, now given in RFC 9989 section 5.3.5 [2], remains the same.

[1] = https://datatracker.ietf.org/doc/html/rfc7489#section-4.2

[2] = https://datatracker.ietf.org/doc/html/rfc9989#section-5.3.5

[daneel_w]

The "logical OR" of DMARC is absolutely a glaring caveat. I run my own MX and would personally under no circumstance omit SPF, because I consider neither SPF nor DKIM complicated enough to warrant consideration.

[aaronmdjones]

This is true, and yet DMARC v1 does not require you to use them in concert. Either one (a valid DKIM-signed message with sender alignment or a message that passes SPF checks with sender alignment) is enough to pass DMARC.

[egorfine]

> The tech industry has a bad habit of providing solutions to problems adjacent to problems the user actually needs solved while leaving the user's actual problem unresolved.

Extremely well said.

[newsoftheday]

My domain is very low traffic but, I just looked through my admin email account and opendmarc has rejected 18 attempts by spammers just this past week. More were rejected by my domain's DMARC policy.

[bcrl]

It works at small scale when you self-select for technical competency. It does not work at larger scale when that self selection is no longer possible.

My scale is that I ran an ISP for ~500 users before the network was disassembled last month. At that scale, you will encounter people that make mistakes with their email setups. When the people who make mistakes are customers which DMARC prevents delivery of emails, it is an issue as those are exactly the people for which I want to see the emails from.

I get more spam with valid SPF and DKIM via Google's own mail servers than DMARC blocks.

It says something when even gmail doesn't use DMARC as a signal that an email is valid, as gmail regularly blocks legitimate mailing list emails with completely valid signatures and non-spam content from a reputationaly sound IP.

The problem DMARC was supposed to solve (impersonation to reduce spam) isn't solved by DMARC.

[SoftTalker]

My work email is Outlook, which is horribly broken and terrible to use. I have a rule configured to "re-send" all my mail to a different account where I read it with a usable MUA. Unfortunately this seems to break DMARC for external mail as now an email from e.g. [e-mail] appears to have been sent by outlook.com.

[matharmin]

I'm not familiar with Outlook's resending, but the use case is supported if the sender uses DKIM. If the email is forwarded without changing any details, it can keep the DKIM signature. That allows the forwarded email to still pass DMARC.

Now if the sender used SPF + DMARC but not DKIM, this does not work, since the sender IP can't be verified with the forwarded email. In that case, the forwarder has to change the from address to prevent the email from failing DMARC and be rejected.

In practice, senders using SPF+DMARC but not DKIM should be quite rare, you see DKIM+DMARC much more often.

[Polizeiposaune]

I have a long-standing email address that forwards to an email system that I run. The operator of the forwarder switched to using Microsoft's mail infrastructure some years ago and the quality of service of the forward has degraded dramatically ever since.

I've often seen messages resent by Microsoft's mail infrastructure with gratuitously broken DKIM signatures, generally due to changes to whitespace that are not anticipated by DKIM's message canonicalization.

I've also seen messages sent by my bank directly to the email system I administer that had broken DKIM signatures apparently due to some sort of antivirus software they had downstream of the DKIM signer.

[ryanbrunner]

Outlook.com also seems to routinely ignore DMARC (it will bounce emails with a DMARC that's report only)

[matharmin]

I never understood the point of the anti-virus adding a message to _outgoing_ emails. Basically "I swear there is no virus in this email I'm sending you, trust me bro".

[SoftTalker]

"We take security seriously."

[Geezus_42]

Stopping spam isn't what DMARC was designed for.

[cookiengineer]

^ this

Additionally, I would probably guess correctly that almost all spam comes from rotating ASNs these days. Aka from companies that do "growth marketing" or other bullshit that isn't a valid business but just... spamming people.

A lot of the domains that fall through the cracks for single-spam-campaigns have been taken over by botnet campaigns, so the actual owners of said domains probably don't know that their website is spamming everyone else.

But the major providers are the culprit, too, here. Gmail, hotmail, microsoft o365, mailgun ... they all don't even enforce SSL from server to server, and let through "sendmail" like spam because the spammers are paying customers to them.

Source: I am maintaining antispam [1] which I am using to combat spam, phishing, and malware campaigns targeting my customer networks.

[1] https://github.com/cookiengineer/antispam