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...
A couple folks have asked me recently about MX records that they don’t understand. These records consist of a single . or they contain localhost or they are 127.0.0.1. In all cases, the domain owners use these records to signal that the domains don’t accept email. What do these records look like? Why do domains do this? In all cases it’s because the domain owners want to signal...
Many deliverability folks stopped recommending publishing SPF records for the 5322.from address to get delivery to Microsoft. I even remember Microsoft saying they were stopping doing SenderID style checking. A discussion on the emailgeeks slack channel has me rethinking that. It started out with one participant asking if other folks were seeing delivery improvement at MS if they added a SPF...
Multiple times over the last few weeks folks have posted a screenshot of Google Postmaster tools showing some percentage of mail failing DMARC. They then ask why DMARC is failing. Thanks to how DMARC was designed, they don’t need to ask anyone this, they have all the data they need to work this out themselves. The DMARC protocol contains a way to request reports when DMARC authentication...
A question came up on the email geeks slack channel about empty from addresses. I asked if they meant the 5321 or 5322 from address which prompted a question about if you could even have a null 5321 from. Yes, you can and it’s commonly used for some types of email. 5321.from is the bounce address, and the domain used in SPF authentication. Null addresses, literally <>, are used for email...
A question came up on the email geeks slack channel (Join Here) about SenderID. They recently had a customer ask for SenderID authentication. We’ve written about it a few times: (Hotmail moves to SPF Authentication and Until it stops moving) but we’ve not actually stated the reasons why in a post. SenderID was basically SPF version 2. It tried to use the same mechanism as SPF to...
When it comes to SPF records there seems to be a lot of confusion. I mean, a decade after I posted it Authenticating SPF is still the most frequently visited post on the site. And, of course, there are hundreds of other pages out there that discuss SPF and what to publish. Still, there are common questions. Most recently I’ve been addressing questions about what SPF records need to be...
A few days ago Laura noticed a bug in one of our in-house tools – it was sometimes marking an email as SPF Neutral when it should have been a valid SPF pass. I got around to debugging it today and traced it back to a bug in the Go standard library. A DNS TXT record seems pretty simple. You lookup a hostname, you get some strings back. Those strings can be used for all sorts of things, but...
I just got some mail claiming to be from “Bank of America <secure@bofasecure.com>”. It passes SPF: Received-SPF: Pass (sender SPF authorized) identity=mailfrom; client-ip=185.235.176.160; helo=bofasecure.com; It passes DKIM: Authentication-Results: mx.wordtothewise.com (amavisd-new); dkim=pass (1024-bit key) header.d=bofasecure.com The visible RFC 822 From address is strictly...
The US National Cybersecurity Assessments & Technical Services Team have issued a mandate on web and email security, including TLS+HSTS for web servers, and STARTTLS+SPF+DKIM+DMARC for email. It’s … pretty decent for a brief, public requirements doc. It’s compatible with a prudent rollout of email authentication. Set up a centralized reporting repository for DMARC failure...
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