Not a new thing, but a nice example just popped up in my inbox on my phone. But FedEx solved their entire phishing problem when they published a strict p=reject DMARC record, right? This didn’t come from fedex.com. It came from another domain that looks vaguely like fedex.com – what that domain is doesn’t matter, as the domain it’s sent from isn’t displayed to...
On Friday I talked a little about DMARC being a negative assertion rather than an authentication method, and also about how and when it could be deployed without causing problems. Today, how DMARC went wrong and a partial fix for it that is coming down the standards pipeline. What breaks? DMARC (with p=reject) risks causing problems any time mail with the protected domain in the From: field is...
We know that legitimate email sent with valid SPF and a DKIM signature often breaks in transit. SPF will fail any time mail is forwarded – via a mailing list, a forwarding service used by the recipient, or just ad-hoc forwarding. DKIM will fail any time the message is modified in transit. That can be obviously visible changes, such as a mailing list tagging a subject header or adding a...
I just added a DMARC validation tool over on tools.wordtothewise.com. You can give it a domain – such as ebay.com – and it will fetch the DMARC record, then explain and validate it. Or you can paste the DMARC record you’re planning to publish into it, to validate it before you go live. If you’ve not seen our tools page before, take a look. As well as DMARC we have a DKIM...
Over the last few weeks I’ve seen a couple people get on mailing lists and make pronouncements about email. It’s great to have opinions and it’s great to share them. But they’re always a little bit right… and a little bit wrong. SPF is dead! This came from the new ESP of an experienced mailer. They were recommending not publishing SPF records because it was “an...
Setting up a DMARC record is the easy bit. Anyone can publish a record in DNS that will trigger reports to them. The challenge is what to do with those reports and now to manage them. DMARC is a complex protocol. It builds on two other protocols, each with their own nuances and implementation issues. I’ve written in the past about what DMARC is, what you need to know to decide if...
ARC – Authenticated Received Chain – is a way for email forwarders to mitigate the problems caused by users sending mail from domains with DMARC p=reject. It allows a forwarder to record the DKIM authentication as they receive a mail, then “tunnel” that authentication on to the final recipient. If the final recipient trusts the forwarder, then they can also trust the...
Dear Laura, I’m a little confused by the term “no auth / no entry”. Gmail and other major receivers seem to be moving towards requiring authentication before they’ll even consider delivery. Does this just mean SPF and DKIM, or does this mean the much more stringent DMARC, as well? Thanks, No Shirt, No Shoes, No What Now? Shirtless & Shoeless, “No auth / no entry” is...
Mail.ru is switching to p=reject. This means that you should special-case mail.ru wherever … Actually, no. Time to change that script. If you operate an ESP or develop mailing list software you should be checking whether the email address that is being used in the From: address of email you’re sending is in a domain that’s publishing p=reject (is a “rejective” email...
Dear Laura, I heard recently that both Gmail and Yahoo will require DMARC authentication in early 2016 or images will be automatically blocked. Is that correct? And if so, do you know when they will be requiring DMARC? A DMARC-Overwhelmed Admin Dear Overwhelmed, There are three things going on here, all of which are related to DMARC but are very different in how it affects mail delivery...
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