Email Authentication lets you demonstrate that you sent a particular email.
Email Repudiation is a claim that you didn’t send a particular email.
SPF is only for email authentication1
DKIM is only for email authentication
DMARC is only for email repudiation
1 SPF was originally intended to provide repudiation, but it didn’t work reliably enough to be useful. Nobody uses it for that now.
Email – and email filtering – makes a lot of use of DNS, and it’s fairly easy to miss something. Here are a few checklists to help:
Read MoreAccording to a recent blog post, Office365 is starting to evaluate incoming messages for DMARC. I talked a little bit about DMARC in April when Yahoo started publishing a p=reject message.
Read MoreA new email industry group was announced this morning. DMARC is a group of industry participants, including large senders, large receivers and relevant intermediaries working on a framework to reduce the harm from phishing.
DMARC is working on a standard to allow senders to publish sending policies and receivers to act on those policies. Currently, senders who want receivers to not deliver unauthenticated email have to negotiate private agreements with the ISPs to make that happen. This is a way to expand the existing programs. Without a published standard, the overhead in managing individual agreements would quickly become prohibitive.
It is an anti-phishing technique built on top of current authentication processes. This is the “next step” in the process and one that most people involved in the authentication process were anticipating and planning for. I’m glad to see so many big players participating.