Who's publishing DMARC?

DMARC is a way for a domain owner to say “If you see this domain in a From: header and it’s not been sent straight from us, please don’t deliver the mail”. If a domain is only used for bulk and transactional mail, it can mitigate a subset of phishing attacks without causing too many problems for legitimate email.
In other cases, it can cause significant problems. Some of those problems impact discussion lists, but others cause problems for ESPs servicing small companies and individuals. ESP customers use their email addresses in the From: field; if they’re a small customer using the email address provided by their ISP, and that ISP publishes a DMARC record with p=reject, a large chunk of the mail they’re sending will bounce. When that happens recipients will stop getting their email, they’ll be removed from the mailing list due to bounces, and there’s some risk of blocks being raised against the sending IP address.
Because of that, it’s good to be able to see what consumer ISPs are doing with DMARC.
I’ve created a tool at dmarc.wordtothewise.com that regularly checks a list of large consumer ISPs and webmail providers and sees what DMARC records they’re publishing.
There are two main variants of DMARC records.
One is policy “reject” – meaning that mail that isn’t authenticated (or for which authentication has been broken in transit) will likely be rejected.
The other is policy “none” – meaning that the ISP publishing the record doesn’t want recipients to change their delivery decisions, but are asking for feedback about their mailstream, and how much of it fails authentication. That can mean that the ISP is evaluating whether or not to publish p=REJECT, or is in the process of deploying p=REJECT. Or it can just mean that they’re using DMARC to monitor where mail using their domain in the From: address is being sent from. There’s no way to tell which is the case unless they’ve made an announcement about their plans.
Hopefully this will be a useful tool to monitor DMARC deployment by consumer ISPs, and to help diagnose delivery problems that may be caused by DMARC.

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DMARC and organizations

Comcast recently published a statement on DMARC over on their postmaster page. The short version is that Comcast is publishing a DMARC record, but has no current intentions to publish a p=reject policy for Comcast user email. Comcast will be publishing a p=reject for some of their domains that they use exclusively to communicate with customers, like billing notices and security notices.
Comcast does point out that Yahoo! and AOL’s usage of p=reject is “not common usage.”
This is something a lot of people have been arguing loudly about on various mail operations lists and network lists. DMARC is about organizational identity. In fact, I was contacted about my DMARC primer and told that I didn’t mention that it’s not about domains, it’s about organizations.
The way I read the DMARC spec, it is all about organizational identity. The underlying theme being that the domain name is linked to a particular organization and everyone using email at that domain has some official relationship with that organization. I’ve always read the spec mentally replacing organization with corporate brand. This was for brands and organizations that strictly control how their domains are used, who can use those domains and how the mail is sent with those domains.
I never expected any mailbox provider or commercial ISP to publish a p=reject message as it would just break way too much of the way customers use email. And it did break a lot of legitimate and end user uses of email. Many organizations have had to scramble to update mailing list software to avoid bouncing users off the lists. Some of these upgrades have broken mailbox filters, forcing endusers to change how they manage their mailboxes.
Even organizations see challenges with a p=reject message and can have legitimate mail blocked. At M3AAWG 30 in San Francisco I was talking with some folks who have been actively deploying DMARC for organizations. From my point of view anyone who wants to publish a DMARC p=reject should spend at least 6 months monitoring DMARC failures to identify legitimate sources of email. The person I was talking to said he recommends a minimum of 12 months.
This is just an example of how difficult it is to capture all the legitimate sources of emails from a domain and effectively authenticate that mail. For a mailbox provider, I think it’s nearly impossible to capture all the legitimate uses of email and authenticate them.
It remains to be seen if the other mailbox providers imitate Yahoo! and AOL or if they push back against the use of DMARC reject policies at mailbox providers. Whatever the outcome, this is a significant shift in how email is used. And we’re all going to have to deal with the fallout of that.

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ReturnPath on DMARC+Yahoo

Over at ReturnPath Christine has an excellent non-technical summary of the DMARC+Yahoo situation, along with some solid recommendations for what actions you might take to avoid the operational problems it can cause.

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Spammers react to Y! DMARC policy

It’s probably only a surprise to people who think DMARC is the silver bullet to fixing email problems, but the spammers who were so abusing yahoo.com have moved on… to ymail.com.
In the rush to deploy their DMARC policy, apparently Yahoo forgot they have hundreds of other domains. Domains that are currently not publishing a DMARC policy. Spammers are now using those domains as the 5322.from address in their emails. The mail isn’t coming through any yahoo.com domain, but came through an IP belonging to Sprint PCS.
ymail_dmarc
This is just one example of how spammers have reacted to the brave new world of p=reject policies by mailbox providers. If only the rest of us could react as quickly and as transparently to the problems imposed by these policy declarations. But changing software to cope with the changes in a way that keeps email useful for end users is a challenge. What is the right way to change mailing lists to compensate for these policy declarations? How can we keep bulk email useful for small groups that aren’t necessarily associated with a “brand”?
The conversation surrounding how we minimize the damage to the ecosystem that p=reject policy imposed hasn’t really happened. I think it is a shame and a failure that people can’t even discuss the implications of this policy. Even now that people have done the firefighting to deal with the immediate problems there still doesn’t seem to be the desire to discuss the longer effect of these changes. Just saying “these are challenges” in certain spaces gets the response “just deal with it.” Well, yes, we are trying to deal with it.
I contend that in order to “just deal with it”, we have to define “IT.” We can’t solve a problem if we can’t define the problem we’re trying to solve. Sadly, it seems legitimate mailers are stuck coping with the fallout, while spammers have moved on and are totally unaffected.
How is this really a win?

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