4 ms·

DMARC is a relatively recent addition to the email security space, and while it seems a bit superfluous at first, is actually quite useful! Sending and receivin

DMARC is a relatively recent addition to the email security space, and while it seems a bit superfluous at first, is actually quite useful! Sending and receiving the reports (which, should be noted, is entirely optional) might indeed be helped by a setup separate from the main mail handling workflow, as the 'best effort' nature and the fact that lots of systems sending DMARC reports have no business delivering mail for the sender domain in the first place are quite distinct. Both Microsoft and Google seem to do it just fine using their main infrastructure though, so there's that. And apart from (performing or hopefully kickstarting) troubleshooting of SPF and (especially) DKIM failures, going through the forensic reports (which not everyone sends, even if they do summaries, due to message privacy concerns) will definitely satisfy your 'WTF-quota' for the day, since you get to see some spoofed messages that are usually just blackholed, and some of those are truly bizarre...

flowerthoughts 10mo ago
I also don't see why the DMARC reporting would retry sending. If the receiver isn't receiving right away, surely it's okay to just drop that report to keep the queue small.
- ZeroConcerns 10mo ago
  We already had 'low effort' mail queues (for things like password reset emails: these are retried 1/2/4/8 minutes apart and don't generate bounces, other than an API flag and a metrics record), to which we added 'least effort' for DMARC reports. Retry once, then forget about the entire thing other than incrementing a counter for the destination domain.
  - jcynix 10mo ago
    > retried 1/2/4/8 Minuten apart That's generally not very clever, as it will impose an unneeded burden on a receiving server which actually has temporary resource problems, and it will collide with greylisting, for example. RFC 5321 states in section "4.5.4.1. Sending Strategy" that the retry interval should be at least 30 minutes, while the give-up time needs to be at least 4–5 days: https://datatracker.ietf.org/doc/html/rfc5321#section-4.5.4 https://datatracker.ietf.org/doc/html/rfc5321#section-4.5.4
    - b112 10mo ago
      SHOULD is not MUST. These capitalized terms are have very specific meanings in RFCs, see RFC https://datatracker.ietf.org/doc/html/rfc2119 https://datatracker.ietf.org/doc/html/rfc2119. SHOULD is: 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. MUST is a requirement. You left out the "however" part: In general, the retry interval SHOULD be at least 30 minutes; however, more sophisticated and variable strategies will be beneficial when the SMTP client can determine the reason for non-delivery. There's absolutely nothing wrong with a fine tuned backoff. I am not saying the specific backoff discussed by GP is best, merely that 30 minutes is absolutely not a requirement, and in fact, discussed in tandem with the fact that "more sophisticated strategies" are actually beneficial. The RFC does not agree with you. Partially quoted as you have, does not help.
    - ZeroConcerns 10mo ago
      > the retry interval should be at least 30 minutes, while the give-up time needs to be at least 4–5 days RFCs have very little to do anymore with the realities of email delivery. And advocating for password reset emails to only be retried after 30 minutes (all while the user is manically mashing the 'resend link' button) and/or to be kept around for 5 days (while the link contained therein expires after an hour) doesn't either.
b112 10mo ago
Both Microsoft and Google seem to do it just fine I routinely get between 5 and 10 duplicates of DMARC reports from Google for gmail. Searching on this, it's a known phenomenon. No one else has this issue. I don't get dupes from outlook.com, hotmail, yahoo, etc, etc. But it's Google. Fairly typical for their modern quality control and engineering practices. I view them as a little like when Volkswagen stopped being run by engineers, and instead by accountants.
- 0x0 10mo ago
  Same here, and the worst part is the duplicates appear to reuse the same Message-id, which confuses macOS Mail.app to no end :-/
34679 10mo ago
>which, should be noted, is entirely optional I wouldn't say entirely. I had a client with a large company contact me on LinkedIn saying that they wanted to buy my product but no one would respond to their emails. Their system was nuking my responses until I set up DMARC reporting, and I had no indication it was happening on my end. No "failed to deliver" message and nothing in the logs, just email that vanished into the ether.
- ZeroConcerns 10mo ago
  That's interesting! Can you share which provider their MX record pointed to? Silently disappearing emails are typical Microsoft Forefront antics (but definitely also a misfeature of other products), but mostly when the originating domain has a p=reject DMARC policy. You didn't happen to relax that at the same time you added the reporting parameters?
- turnsout 10mo ago
  But once your DMARC, DKIM & SPF is configured correctly, there should be no reason for an MTA to reject your mail due to DMARC, right? I have DMARC reporting turned on, but am considering turning it off.
  - toast0 10mo ago
    Back when I ran email for a large sender, I turned DMARC reports off once I got things settled in, and might turn it on to debug issues. There was nothing to do about the reports most of the time. Just get mad that people are accepting spoofed mail that fails DKIM and SPF. But mostly, the phishing campaigns with our branding just stopped spoofing addresses. Turns out, lots of email clients don't show the sender address and people who get a phishing email about Service Y from info@johnsplumbingservices.example.com may get phished.
nemetroid 10mo ago
> Both Microsoft and Google seem to do it just fine Microsoft sends me DMARC reports saying "yes, everything was accepted 100%, all good". The delivery logs on our end look good as well. However, they silently drop a large portion of messages with a Hotmail destination.
- ZeroConcerns 10mo ago
  Yeah, there is a whole layer of Rube Goldberg-esque nonsense between the public Microsoft SMTP servers and the actual destinations that not even the highest levels of their support seem to properly understand. Like: if you truly want to ensure delivery to an Office 365 tenant, EWS is pretty much the only option. Anything else will have random gaps, even after the tenant themselves have begged everyone they could find to let that particular sender, domain, IP, and everything through no matter what...
brightball 10mo ago
It's been pretty mainstream since 2012 IIRC. The article is correct though. Microsoft has never done it just fine. Their reports are constantly interrupted and at one point it lasted years. Microsoft also wasn't following spec on handling DMARC rules and would take failed messages with a reject policy that should have been dropped and then put them in the spam folder, creating massive phishing risk. I believe they have finally started to get their act straight but for a long time they were the biggest problem in the space. Google has usually been one of the leaders in the DMARC space though. Yahoo too.

flowerthoughts 10mo ago

I also don't see why the DMARC reporting would retry sending. If the receiver isn't receiving right away, surely it's okay to just drop that report to keep the queue small.

ZeroConcerns 10mo ago
We already had 'low effort' mail queues (for things like password reset emails: these are retried 1/2/4/8 minutes apart and don't generate bounces, other than an API flag and a metrics record), to which we added 'least effort' for DMARC reports. Retry once, then forget about the entire thing other than incrementing a counter for the destination domain.
- jcynix 10mo ago
  > retried 1/2/4/8 Minuten apart That's generally not very clever, as it will impose an unneeded burden on a receiving server which actually has temporary resource problems, and it will collide with greylisting, for example. RFC 5321 states in section "4.5.4.1. Sending Strategy" that the retry interval should be at least 30 minutes, while the give-up time needs to be at least 4–5 days: https://datatracker.ietf.org/doc/html/rfc5321#section-4.5.4 https://datatracker.ietf.org/doc/html/rfc5321#section-4.5.4
  - b112 10mo ago
    SHOULD is not MUST. These capitalized terms are have very specific meanings in RFCs, see RFC https://datatracker.ietf.org/doc/html/rfc2119 https://datatracker.ietf.org/doc/html/rfc2119. SHOULD is: 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. MUST is a requirement. You left out the "however" part: In general, the retry interval SHOULD be at least 30 minutes; however, more sophisticated and variable strategies will be beneficial when the SMTP client can determine the reason for non-delivery. There's absolutely nothing wrong with a fine tuned backoff. I am not saying the specific backoff discussed by GP is best, merely that 30 minutes is absolutely not a requirement, and in fact, discussed in tandem with the fact that "more sophisticated strategies" are actually beneficial. The RFC does not agree with you. Partially quoted as you have, does not help.
  - ZeroConcerns 10mo ago
    > the retry interval should be at least 30 minutes, while the give-up time needs to be at least 4–5 days RFCs have very little to do anymore with the realities of email delivery. And advocating for password reset emails to only be retried after 30 minutes (all while the user is manically mashing the 'resend link' button) and/or to be kept around for 5 days (while the link contained therein expires after an hour) doesn't either.

b112 10mo ago

Both Microsoft and Google seem to do it just fine I routinely get between 5 and 10 duplicates of DMARC reports from Google for gmail. Searching on this, it's a known phenomenon. No one else has this issue. I don't get dupes from outlook.com, hotmail, yahoo, etc, etc. But it's Google. Fairly typical for their modern quality control and engineering practices. I view them as a little like when Volkswagen stopped being run by engineers, and instead by accountants.

0x0 10mo ago
Same here, and the worst part is the duplicates appear to reuse the same Message-id, which confuses macOS Mail.app to no end :-/

34679 10mo ago

>which, should be noted, is entirely optional I wouldn't say entirely. I had a client with a large company contact me on LinkedIn saying that they wanted to buy my product but no one would respond to their emails. Their system was nuking my responses until I set up DMARC reporting, and I had no indication it was happening on my end. No "failed to deliver" message and nothing in the logs, just email that vanished into the ether.

ZeroConcerns 10mo ago
That's interesting! Can you share which provider their MX record pointed to? Silently disappearing emails are typical Microsoft Forefront antics (but definitely also a misfeature of other products), but mostly when the originating domain has a p=reject DMARC policy. You didn't happen to relax that at the same time you added the reporting parameters?
turnsout 10mo ago
But once your DMARC, DKIM & SPF is configured correctly, there should be no reason for an MTA to reject your mail due to DMARC, right? I have DMARC reporting turned on, but am considering turning it off.
- toast0 10mo ago
  Back when I ran email for a large sender, I turned DMARC reports off once I got things settled in, and might turn it on to debug issues. There was nothing to do about the reports most of the time. Just get mad that people are accepting spoofed mail that fails DKIM and SPF. But mostly, the phishing campaigns with our branding just stopped spoofing addresses. Turns out, lots of email clients don't show the sender address and people who get a phishing email about Service Y from info@johnsplumbingservices.example.com may get phished.

nemetroid 10mo ago

> Both Microsoft and Google seem to do it just fine Microsoft sends me DMARC reports saying "yes, everything was accepted 100%, all good". The delivery logs on our end look good as well. However, they silently drop a large portion of messages with a Hotmail destination.

ZeroConcerns 10mo ago
Yeah, there is a whole layer of Rube Goldberg-esque nonsense between the public Microsoft SMTP servers and the actual destinations that not even the highest levels of their support seem to properly understand. Like: if you truly want to ensure delivery to an Office 365 tenant, EWS is pretty much the only option. Anything else will have random gaps, even after the tenant themselves have begged everyone they could find to let that particular sender, domain, IP, and everything through no matter what...

brightball 10mo ago

It's been pretty mainstream since 2012 IIRC. The article is correct though. Microsoft has never done it just fine. Their reports are constantly interrupted and at one point it lasted years. Microsoft also wasn't following spec on handling DMARC rules and would take failed messages with a reject policy that should have been dropped and then put them in the spam folder, creating massive phishing risk. I believe they have finally started to get their act straight but for a long time they were the biggest problem in the space. Google has usually been one of the leaders in the DMARC space though. Yahoo too.