DKIM2 and DMARCbis Have Landed

https://stalw.art/blog/dkim2-dmarcbis/

by StalwartLabs • 16 days ago

94 96 16 days ago

stalw.art

meysamazad• 16 days ago

well done

you're among the first few who have done it:

https://github.com/mjl-/mox/issues/404#issuecomment-43627498...

jeroenhd• 14 days ago

First time I'm reading about this, I'm glad there's progress in this area.

The JSON DSL for rewriting emails feels like a spammer/exploit vector waiting to happen. Some product is going to spam filter before applying reconstruction rules, or get tricked into applying reconstruction rules when it shouldn't, and spammers and scammer are going to abuse it.

Until either Google or Microsoft will adopt these standards, they'll remain effectively meaningless most likely. But even so, it's good to know people haven't given up on fixing email's spam problem entirely.

qurren3• 14 days ago

Aw hell. How many things do I have to set up just so that I can send e-mails from my own domain?

The effect of all this seems to be less "making e-mail secure" and more "making it so that only Google, Apple, and Microsoft can send e-mail successfully"

doubled1124• 14 days ago

And sometimes if you do everything right, it still doesn’t work.

Recently I checked the IP against blacklists, waited a few months, did all of the other things, and then found out Microsoft bounces my entire VPS’s IP range. Appealing did not help.

They intermittently block Cloudflare email routing IPs too. All of these security measures and still it comes down to the IP address of your sender.

1over137• 14 days ago

Is it an el cheapo VPS?

braiamp3• 14 days ago

Eh, I read the article, and at most you only have to wait for your MTA to update to add the required headers and update your DNS records and you are golden. It still uses the same key you generated as far I'm aware.

brightball5• 14 days ago

DMARC isn't for sending email successfully, it's for preventing other people from impersonating your domain. Without it, there's nothing stopping anybody from sending an email saying it is from you@qurren.com. SPF tried. DKIM tried. Both of them had gaps.

When you use them together and have a DMARC policy that requires one of them or the other for successful delivery, it's the best current solution.

qurren3• 14 days ago

Except I think I've had 1:1 personal e-mails from my domain go into a legitimate recipient's spam filter just because I didn't have DMARC set up and their mail server was flagging that "DMARC not set up == spammy domain"

TZubiri5• 14 days ago

Right, and when you don't configure DMARC successfully and the recipient requires DMARC, then you cannot send email successfully.

OneDeuxTriSeiGo• 14 days ago

DKIM2 and DMARCbis are actually the opposite of this. They are long awaited fixes of brittle and often broken systems that are designed to now make providing secure email easier rather than harder.

They both have fairly clean migration paths and resolve a lot of the annoying edge cases that currently exist with authenticating and verifying email.

binkHN• 14 days ago

Thanks for this, it made me actually read the posted content, but there's a lot of content to digest and a lot MTAs will have to implement.

AceJohnny22• 14 days ago

Aw hell. How many things do I have to set up just so that I can send e-mails from my own domain?

... said every spammer.

I'm sorry for your pain, and I'm in the same boat.

But it's important to understand that any sufficiently large, distributed-agent system (like federated email), will see the rise of parasites that will pump resources and diminish the value of the system.

What we're seeing here is an "immune" response to those parasites. We all pay for it.

I think this is an important lesson for anyone designing a distributed-agent system [1]. How do you design it so as to keep the bad actors out, or at least so their impact is negligeable?

[1] imma make my own email system! With blackjack, and hookers! oh wait...

assimpleaspossi• 14 days ago

>parasites that will pump resources and diminish the value of the system.

Countries' legal systems really need to do something about them.

hinkley• 14 days ago

This sort of Regulatory Capture is quite old in the software field. People were already noticing it in the 90's.

Making a spec that contains a venn diagram of most of the features each of the signatories to the specification have implemented themselves ends up pulling the ladder up behind them. Each non-academic committee member discovers they're already more than 75% of the way to having completed the spec and any junior members or amateurs have years of work to do in order to catch up to Now. If any upstarts threaten to get within striking distance of an implementation you can always convene the committee again and discuss version 2 of the spec.

Mobile devices tamped this down just a little bit but mostly they lowered the slope of the line a hair and changed where the focus was a bit.

lousken• 14 days ago

Anyone migrated from exchange to stalwart? Curious about results

bigbuppo• 14 days ago

Can someone distill this down to how it will be used by the big three email providers to make it impossible to use email except through them?

braiamp3• 14 days ago

If anything, this moves it towards anyone having more access to everything. For example, reject isn't going to be treated anymore as a bounce. Now, provider policies still can and would be BS, but the standard doesn't tell them to do it certain way.

TacticalCoder• 14 days ago

by the big three

Which big three?

Gmail has something like 1.8 billion users. iCloud mail around 1 billion.

Microsoft with 400 million users of its email is closer to Yahoo! Mail (225 million users) than to the big two.

AlotOfReading• 14 days ago

User numbers aren't the only factor. Microsoft has a much larger presence in commercial email than Apple. I suspect an outbound email from a personal provider is far more likely to be destined for an outlook inbox than one on iCloud.

braiamp3• 14 days ago

Despite what everyone said, I'm excited specifically for DKIM2. As someone that had managed a mailing list, that one is probably the hardest thing to juggle around and DKIM2 layering seems to fix that issue neatly. I hope postfix has a guide proto.

dataflow4• 14 days ago

I really don't understand what the original DKIM was not sufficient. Can someone ELI5? If you can verify that a message (including headers, which DKIK can sign) was signed by the outgoing server, then why isn't that the end of the story? Who cares how or why it got forwarded, or whatever else?

brightball5• 14 days ago

There are a few gaps with DKIM.

1. You have to set it up on every sending server. It's easier today but it wasn't always

2. You have to periodically rotate each of the keys that you setup because they can be cracked/stolen. Soon as somebody steals your key, they can impersonate anyone sending email from your domain.

3. Receiving email servers have no way of knowing if a message they received without a DKIM signature is supposed to include a DKIM signature, so simply not including one creates a scenario where receiving mail servers have to guess if the message was really from you.

crote• 14 days ago

2b. You have to publish the retired private keys, or else a recipient will retain undeniable proof of message authenticity.

Depending on your perspective, this can be either a feature or a bug.

dataflow4• 14 days ago

1. I can't say I buy this excuse, but okay.

2. Is this an actual problem that has arisen with a worrying frequency in the past, or just a hypothetical? And how is it different from someone stealing your SSH key or TLS certificate?

3. Isn't it obvious from previous emails you've received from the same server?

yasaheblasa4• 14 days ago

1&2 sound worse after this update as described.. I'm not really sure why we are still bothering with this when DNSSEC progress means DANE like setups could solve the original E2E S/MIME issues of payment and domain indicating expectation of what its email senders are required to have for S/MIME.

There are some aspects of (possibly positive) deniability by an individual that probably still remain with DKIM but they kind of remain anyway with domain anchored S/MIME.

bawolff4• 14 days ago

Who cares how or why it got forwarded, or whatever else?

Because it broke enough niche usecases that lots of people didn't feel comfortable fully turning on dmarc in strict mode. Fixing that will hopefully spike adoption

winstonwinston• 14 days ago

They want to allow forwarders (such as mailing lists) to modify signed messages all while keeping the original signed author email address. It is meant to replace ARC which is now deprecated.

You can now verify who changed what and when but it is still based on will and trust to accept what has been altered and therefore a security theatre.

It ‘solved’ a problem for a mailing list that insist on altering signed messages, even though they do not have to modify forwarded messages in my opinion and many lists do not.

stefan_lec• 14 days ago

Sounds pretty cool! I wonder if it closes enough holes that we could finally stop using SPF at all?

peanut-walrus2• 14 days ago

Missed opportunity to get rid of SPF. What I want to my DMARC policy to say: if someone is sending you an email that claims to be from my domain and it's not signed by one of the keys I have published under my domain, you should reject it, regardless where it came from.

And on the receiving side, the policy is similarly simple: if I receive any unsigned or unaligned email, I will reject it.

Edit: to clarify, I want there to be an option where I specify my DMARC policy to explicitly tell well-configured receiving servers "ignore whatever I have configured as my SPF record, only look at the signatures". There will no doubt be a long tail of mail servers where I will still need an SPF record for them to accept my mail.

Edit2: Another feature that I feel is lacking is ability to give dkim selectors a scope - e.g. this key is only valid for these particular From addresses.

AceJohnny22• 14 days ago

I suspect SPF is used because it's cheaper than performing cryptographic checks for each email. A (cached) DNS lookup and IP check on a connection is comparatively cheaper.

justusthane• 14 days ago

Isn’t that already what DMARC does though? For DMARC to pass you need DKIM _or_ SPF alignment, not both. It’s designed that way because there are scenarios where SPF _can’t_ pass (email forwarding, mailing lists). So a well-configured mail server should accept your email regardless of SPF if DKIM is properly configured.

Re: specific keys for specific usernames: I can appreciate that you wish DKIM allowed for this, and I could imagine it being handy, but that was never the problem DKIM set out to solve — DKIM and SPF are all about be domain.

I’m also not sure it’s a great idea — the sender identity should be under the control of the sender. If you control the domain @foo.com, you could use that ability to assert that an email came from Bob, even if Bob never sent it. Contrast that with Bob signing the email using his own private key.

reader9274• 14 days ago

Isn’t that already what DMARC does though? For DMARC to pass you need DKIM _or_ SPF alignment, not both.

But now if SPF passes and is aligned, DMARC passes (it doesn't matter what DKIM's status is). OP here wants to complete skip the SPF check entirely.

toast02• 14 days ago

Isn’t that already what DMARC does though? For DMARC to pass you need DKIM _or_ SPF alignment, not both.

GP wants require DKIM, so SPF alone is insufficient to send mail from their domains.

If everyone did dmarc, you could set SPF to -all. But there are servers that check SPF but not DMARC. You need to pass SPF for those, so you need a passable SPF... but then DMARC will pass with only SPF.

ericpauley• 14 days ago

Best way to go about this is just blackhole SPF so it never passes, then set your DMARC alignment to strict. This approach prevents SPF from satisfying DMARC on the vast majority of providers [1].

[1] https://taejoong.github.io/files/publications/hamza-2026-dma...

peanut-walrus2• 14 days ago

In theory, yes, in practice this will currently result in deliverability issues, both for servers which don't speak dmarc and for spam signals. I have tried this :)

If this mode of operation was an explicit choice, this would give me the option to have a fallback SPF record for legacy mail systems, but most up-to-date servers will use the more secure and (for my use case) operationally simpler verification.

inigyou4• 14 days ago

And I want mine to say: if it comes from my MX server it's legit, don't worry about the keys.

Because that's easy and keys and signing are hard.

TZubiri5• 14 days ago

Missed opportunity to get rid of SPF.
you should reject it, regardless where it came from.

Just don't use it yourself then?

"v=spf1 ?all"

drhagen• 14 days ago

They spent a huge amount of complexity supporting mailing lists that claim mutated messages came FROM the original sender instead of FROM mailinglist@example.com. Is that use-case worth the additional effort?

bombcar4• 14 days ago

Yes. Mailing lists are incredibly useful and very hard to change.

edelbitter4• 14 days ago

Yes! Forwarding is the reason mail flow authentication does not work very well today. Fix the forwarding use cases (and by extension: mailing lists & out of office arrangements) and we can finally just tell all senders: "Your domains do not match, please use DMARC so we can automatically detect whether that is OK. No excuses, no exemptions, your use case can be dealt with using DMARC!"

edoceo2• 14 days ago

Maybe it's time to call it CMTP

toomim• 14 days ago

Complex Message Transfer Protocol

edoceo2• 14 days ago

Correct.

Animats• 14 days ago

Questions:

- How much infrastructure has to be fixed before this works, and in what order?

- Can you send mail from something that doesn't have a DNS entry? How does this affect the first hop from a desktop or mobile SMTP client?

- If an spam email came via SendGrid, Constant Spammer, or MailChump, are you going to be able to tell from the header signatures?

- If your headers are correct, are you guaranteed mail bounces for un-deliverable emails?

zbentley3• 14 days ago

Can you send mail from something that doesn't have a DNS entry?

I hope not. Just like SSL, I think requiring a registrar+DNS server to vouch for a durable identity is an important barrier to abuse (and an important intervention point for violation reports).

edelbitter4• 14 days ago

Can you send mail from something that doesn't have a DNS entry?

You never really could. Participating in public email exchange requires that the sender can resolve then "fully qualified" domain in your return address. Except after prior agreement or authentication, messages simply that fail this are not generally accepted.

If your headers are correct, are you guaranteed mail bounces for un-deliverable emails?

Even better: You are more likely to see an immediate refusal instead of a delayed bounce, if the recipient exchange can during transmission already determine that they do not want message claiming to be originally transmitted from X to Y yet breaking their ability to check the signature added by X.

TZubiri5• 14 days ago

You never really could.

You can, open a TCP socket on port 25 to $IP, and just start sending email headers.

You can also use local domains, no DNS.

You can also leave a file in the /var/mail directory with the filename of the user.

toast02• 14 days ago

You never really could. Participating in public email exchange requires that the sender can resolve then "fully qualified" domain in your return address.

I thought you could send from <> for things that shouldn't bounce.

bawolff4• 14 days ago

If an spam email came via SendGrid, Constant Spammer, or MailChump, are you going to be able to tell from the header signatures?

Couldn't you always tell this from headers? At the very least the recieved headers are going to be a give away.

SXX2• 14 days ago

What always bugged me about whole email its that we still dont have two best and most reasonable practice to fight about abuse:

1 - Ability to pay once to provider give your domain Good reputation score to new or old domain and IP and whatever. Like pay once, be a good citizen.

2 - Or just use Hashcash or any other PoW.

This would really solve a problem with 99.9% of spam and allow actually more decentrolized email system.

Fact that no matter what you do its impossible to setup own emaik server to just send few emails a year with 100% guaranteed delivery is just beyond me.

edelbitter4• 14 days ago

In a way, the "let the money decide who is a good citizen" already works. Just not in our favor: Most of the spam I receive is not from some rando using an IP I know nothing about. Its from providers that keep making good money with their current anti-abuse.. strategy. As much as I would like, I cannot refuse all mail from certain providers, because some of their customers are "important" and non-abusive. But I get the good and the bad all laundered together¹.

¹) Some do allow recipients to distinguish, e.g. Sendgrid add an X-Entity-ID header which is a stable 1:1 or <small-number>:1 map between short ascii identifiers and customers. So if you store that mapping, you can reject the usual "From: <admin@bigcorp.example> but not sent using the account associated with bigcorp.example". (The way they easily could, if they cared.)

bawolff4• 14 days ago

Or just use Hashcash or any other PoW.

People love the idea of this, but i don't think it really makes sense.

How high do you set the PoW to? I dont think there is any middle ground that would actually deter attacks but not deter legit users.

SXX2• 14 days ago

When I have personal email server and I need just ocasionally send email or two it can be as high as possible.

I just want them delivered not into Spam folder.

comex• 14 days ago

I wonder how this post was composed. It's full of LLM-isms, but is also pretty informative and not too fluffy - basically, higher-quality than I'm used to seeing from LLM blog posts, especially at this length. Perhaps it was composed based on a detailed human outline? Or perhaps, could this be the power of Fable?

flowerthoughts• 14 days ago

Getting rid of ARC would be so nice, but of course this just means I need to add DKIM2 and need ARC for backwards compatibility.

DKIM2 and DMARCbis Have Landed

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