Why Yahoo Mail is Broken – the Yahoo DMARC Bouncing Rejection Thing Explained

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If you use a Yahoo email address, or are on a Yahoo mailing list, then you may already know that recently Yahoo essentially broke countless mailing lists, and generally made a lot of email broken, as any email with a “from Yahoo” address that wasn’t sent through a Yahoo mail server was rejected.

Screen shot of stories about Yahoo breaking email – we especially like the “Yahoo Killt Mailinglisten”

yahoo kills mailing lists with dmarc


Here is what happened, in a nutshell:

DMARC (Domain-based Message Authentication, Reporting and Conformance) is an authentication mechanism that helps receiving email systems to authenticate the origin of an email, and how legitimate it is.

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Why Yahoo Mail is Broken – the Yahoo DMARC Bouncing Rejection Thing Explained

DMARC, like other authentication mechanisms such as SPF, is published so receiving mail systems can “read” it as the email is being handed from server to server. It sets policies by which a receiving mail server can determine the authenticity of email that is being received at the server.

Last week Yahoo published their DMARC policy to say, in essence, “if you receive email coming from an @yahoo.com address, but it doesn’t come from a yahoo.com mail server, you should reject it.” In DMARC language, this is indicated as “p=reject”.

Of course, this immediately broke email for anybody using a Yahoo email address, but sending email through another (non-yahoo) mail system. And in this day and age, lots and lots of people don’t log in to their webmail account in order to send email as their webmail email address.

And because Yahoo hosts countless mailing lists, this also had the effect of breaking any mailing list mail that people were using their Yahoo addresses on, but not actually sending through the Yahoo servers.

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So, what should you do if you use a Yahoo email address as your primary email address?

Well, as we see it, you have two options: 1) always log into Yahoo to send your email, or 2) take the hint that it’s finally time to switch over to a different email address.

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Why Yahoo Mail is Broken – the Yahoo DMARC Bouncing Rejection Thing Explained

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