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Anatomy of a Received header

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...

Looking back, looking forward

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...

Errors in DKIM records

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...

One-click unsubscribe

The worst thing about the yahoogle requirements has been their use of the term “one-click unsubscribe”. It’s an overloaded term that’s being used here to mean RFC 8058 in-app unsubscription. That’s a completely different thing to what one-click unsubscription has been used to mean for decades, often in the context of complying with legal requirements around...

Don’t trust Gmail’s Show Original

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...

Are you a grown-up sender?

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...

Yahoogle FAQs

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: and :

About My Email

Happy 2024, everyone! We’ve released a shiny new tool to let folks self-check a lot of common questions we see about email requirements. Go to AboutMy.email and send an email to the email address it gives you. Once it receives that email it will go through it and do many of the basic checks we’d usually do to check the technical health of a client’s email1AboutMy.email is a...

Yahoogle Requirements Update

Since I wrote about it last month the requirements for bulk senders to Yahoo and Google have changed a little.

The big change is that bulk senders need to authenticate with both SPF and DKIM, rather than SPF or DKIM. Only one of those has to align with the 822 From: header.

Can you STARTTLS?

Email supports TLS (Transport Layer Security), what we used to call SSL. Unlike the web, which split it’s TLS support off into a completely different protocol – https, listening on port 443 vs http listening on port 80 – SMTP implements it inside it’s non-encrypted protocol. A mailserver advertises that it supports this by having the word “STARTTLS” in the...

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