Lots of times I see someone asking a question and they talk about their sending domain. And it’s sometimes not 100% clear which domain they mean by that – and when we’re talking about alignment and reputation it can make a difference. So here’s a list of (some of?) the different places a mailserver uses a domain. Hostnames Machine Hostname: What the operating system...
DMARC is the newest of the authentication protocols. It compares the domain in the From: address to the domains authenticated by SPF and DKIM. If either SPF or DKIM pass and they are in the same organizational domain as the domain in the From: address then the email is authenticated with DMARC. I wrote A Brief DMARC primer back in 2014 – when Yahoo deployed p=reject late on a Friday and...
I wrote last year about using “stunt” nameservers for customer subdomain authentication – i.e. dynamically generating all the authentication records needed in DNS for each customer as needed. For example, if you’re an ESP that has customers who can’t or won’t use their own domains and you still need to give them unique subdomains you can generate CNAME records...
EDIT: Now with a production-ready implementation I talk about more here. On Tuesday I wrote about using DNS wildcards to implement customer-specific subdomains for email authentication. As I said then, that approach isn’t perfect. You’d much prefer to have per-customer domain authentication, where each customer has their own DKIM d= and ideally their own SPF records, rather than...
If you’re an ESP with small customers you may have looked at the recent Google / Yahoo requirements around DMARC-style alignment for authentication and panicked a bit. Don’t impersonate Gmail From: headers. Gmail will begin using a DMARC quarantine enforcement policy, and impersonating Gmail From: headers might impact your email delivery.…For direct mail, the domain in the...
When you query DNS for something you ask your local DNS recursive resolver for all answers it has about a hostname of a certain type. If you’re going to a website your browser asks your resolver for all records for “google.com” of type “A”1or “AAAA”, but that’s not important right now and it will either return all the A records for google.com it has...
Another day, another ESP telling a client to publish a SPF include for the wrong domain. It shouldn’t annoy me, really. It’s mostly harmless and it’s just an extra DNS look up for most companies. Heck, we followed Mailchimp’s advice and added their include to our bare root domain and it’s not really a huge deal for companies with only a couple SaaS providers. Still...
Right at the end of January, Microsoft appears to have made couple of changes to how they’re handling authentication. The interesting piece of this is that, in both cases, Microsoft is taking authentication protocols and using them in ways that are slightly outside the spec, but are logical extensions of the spec. The first is an extension of DMARC. They’re rolling out inbox flags for...
At the end of last year, Steve wrote a post about the different types of authentication. I thought I’d build on that and write about the costs associated with each type. While I know a lot of my readers are actually on the sending side, I’m also going to talk about the costs associated with the receiving side and a little bit about the costs for intermediaries such as CRM systems or...
Some notes on some of the different protocols used for authentication and authentication-adjacent things in email. Some of this is oral history, and some of it may be contradicted by later or more public historical revision. SPF Associates an email with a domain that takes responsibility for it. Originally Sender Permitted From, now Sender Policy Framework. It allows a domain owner to announce...
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