[Discuss] DMARC issue, Yahoo and beyond

[Ernest Horne]

I'm a bit out-of-step on current email practice, so for the benefit of other who don't swim in the SMTP stream, I'll quote from the PCWORLD article mentioned:

The problem is a new DMARC (Domain-based Message Authentication, Reporting and Conformance) “reject” policy advertised by Yahoo to third-party email servers, said John Levine, a long-time email infrastructure consultant and president of the Coalition Against Unsolicited Commercial Email (CAUCE), in a message sent to the Internet Engineering Task Force (IETF) mailing list Monday.
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>DMARC is a technical specification for implementing the SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail) email validation and authentication mechanisms. These technologies were designed to prevent email address spoofing commonly used in spam and phishing attacks.
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>The goal of DMARC is to achieve a uniform implementation of SPF and DKIM among the top email service providers and other companies that want to benefit from email validation.
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>The specification introduces the concept of aligned identifiers, which requires the SPF or DKIM validation domains to be the same as or sub-domains of the domain for the email address in the “from” field. The domain owners can use a DMARC policy setting called “p=" to tell receiving email servers what should happen if the DMARC check fails. The possible values for this setting can be "none” or “reject.”
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>Over the weekend Yahoo published a DMARC record with “p=reject” essentially telling all receiving email servers to reject emails from yahoo.com addresses that don’t originate from its servers, Levine said.
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>While this is a good thing from an anti-spoofing perspective, it raises problems for legitimate mailing lists, according to the email expert.
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>“Lists invariably use their own bounce address in their own domain, so the SPF doesn’t match,” Levine said. “Lists generally modify messages via subject tags, body footers, attachment stripping, and other useful features that break the DKIM signature. So on even the most legitimate list mail like, say, the IETF’s, most of the mail fails the DMARC assertions, not due to the lists doing anything ‘wrong’.”
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>With the new policy, when a Yahoo user sends an email to a mailing list, the list’s server distributes that message to all subscribers, changing the headers and breaking DMARC validation. List subscribers with email accounts on servers that perform DMARC checks, such as Gmail, Hotmail (Outlook.com), Comcast or Yahoo itself, will reject the original message and respond back to the list with automated DMARC error messages.
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>I don't think the "blowback" problem applies to the BLU, since (IIRC), the Mailman server diverts any administrative messages. However, other (smaller) lists may be affected, and there's the real risk that YaGooHotCast will all start rejecting each others' mail. 
On Friday, May 16, 2014 9:04 AM, Edward Ned Harvey (blu) <blu at nedharvey.com> wrote:
 


> From: discuss-bounces+blu=nedharvey.com at blu.org [mailto:discuss-
> bounces+blu=nedharvey.com at blu.org] On Behalf Of Stephen Ronan
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> "You may notice a small difference in the From field on list
> messages from these senders (and now from AOL senders too), in
> which the sender's actual email address no longer appears,
> replaced by the address of the list itself.

That is the sympa equivalent of mailman "from_is_list" reply-to munging.
http://wiki.list.org/display/DEV/DMARC

Which seems to be the mailman recommended solution.

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Of course, there's an unspoken reality here: YaGooHotCast administrators are only human, and this might be a reaction to the ever-growing tsunami of spam they have to deal with every day. Given the lack of a FUSSP, the users may be demanding that they do /anything/ instead of just /something/. 

Bill Horne

P.S. Full disclosure: I've known John Levine for years. He provides invaluable support for the Telecom Digest, where I'm the Moderator.