I’ve seen a bunch of folks panic about some phrasing in Google’s Email sender guidelines. Buried deep in the Message formatting section Google say: Don’t use HTML and CSS to hide content in your messages. Hiding content might cause messages to be marked as spam. Read literally that might cause you to wonder about your use of CSS display:none to switch between different content on desktop and mobile. But that’s not what Google are concerned about – they’re targeting spammers who load up their mail with hidden text (“hashbusters“) in an attempt to make the content of the mail look like one thi ..read more

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 to support white label DKIM authentication: selector._domainkey.customerid.espcustomer.com CNAME \selector.dkim.esp.com or generate white label DMARC with useful rua= reporting: _dmarc.customerid.espcustomer.com TXT \ "v=DMARC1 p=n ..read more

We just got back from Amsterdam a couple of days ago, after attending the Deliverability Summit. It may have been the best email event I’ve been to in several years. Not too big, not too small. Plenty of space and time to meet up with folks. Mostly great sessions, a better average than most conferences. Well organized, at a lovely location, with a safe and welcoming environment. Andrew et al. did a great job putting it together. A better return on time and effort than some of the bigger conferences. Keep an eye out for it next year; maybe we’ll see you there ..read more

When trying to find out why Something Went Wrong during delivery of an email we sometimes want to look at the route by which it was delivered. Did SPF break because of an unexpected forward? Did DKIM break because an intermediate mailserver modified the content of the message? Why did it take nine hours from the mail leaving our ESP to make it to the inbox? Did it really leave our ESP when they say it did? Did Microsoft internal handoffs break something again? Received headers are the breadcrumbs that record the path an email took. Every time a mailserver receives an email it adds a Received h ..read more

Six years ago today I wrote here “Spam isn’t going away“, talking about systemic problems at Google, Cloudflare and Amazon and in India. If I were writing it today I might mention Microsoft, Salesforce and ExactTarget as well as Google, and might stress Amazon less (mostly because all the Amazon spam sites tend to be hidden behind Cloudflare, so you don’t know they’re Amazon sites). And OVH, of course. But the gist of the story hasn’t changed in six years, and the conclusion is as valid today as it was then: There will be increasing volumes of B2B spam being sent for the foreseeable future, an ..read more

TXT Records DKIM public keys live in DNS TXT records. A DNS TXT record contains strings of text, and each string is limited to be no more than 255 characters long. Recommended practice for DKIM at the moment is to use 2048 bit keys (1024 bit keys aren’t insecure, but they’re looking a bit weak and 2048 is where folks have mostly decided to move to). But a 2048 bit DKIM key is going to be around 400 characters long. So how do we fit that into a TXT record? A TXT record can contain more than one string, so we can split the 400 character public key into two strings, put both of those strings in a ..read more

It’s not always easy to know what the actual headers and body of an email as sent look like. For a long time accepted wisdom was that you could send a copy to your gmail account, and use the Show Original menu option to, well, see the original message as raw text. It turns out that’s not actually something you can trust. I used swaks to send a test message with an extra header to my gmail account. swaks --to wttwsteve@gmail.com --from steve@blighty.com --add-header "List-Unsubscribe: =?us-ascii?Q?=3Cmailto=3Asteve=40blighty.com=3e?="Code language: JavaScript (javascript) We can see swaks ..read more

Yes, it’s another yahoogle best practices post. Google divide their requirements for senders into those sending more than 5,000 messages a day, and those sending less. Yahoo divide their requirements into “All Senders” and “Bulk Senders”, and explicitly don’t define that via a volume threshold: “A bulk sender is classified as an email sender sending a significant volume of mail. We will not specify a volume threshold.”. So … do you need to count how many messages you send, to see if Google thinks you’re a bulk sender or not? No. Definitely not. Google state a threshold just so they don’t have ..read more

Just a very, very short post with links to the Yahoo and Google requirements FAQs. Given I can’t ever remember them I’m guessing lots of y’all can’t either. Yahoo: https://senders.yahooinc.com/best-practices/ and https://senders.yahooinc.com/faqs/ Google: https://support.google.com/a/answer/14229414 ..read more

On January 9th at 6pm GMT, 1pm EST and 9am PST I’ll be speaking with Nout Boctor-Smith of Nine Lives Digital about the new Yahoo and Google technical requirements. In this webinar you’ll: Learn more about what these new email sender guidelines entail and how they differ from the status quo  Understand why you’re being asked to do things that were previously handled by your ESP (email service provider) Discover what adjustments you can make now to ensure your emails reach their intended inboxes in 2024 We know folks have a lot of questions about these changes and how to comply with them ..read more