Spam Resource: All Things Deliverability
I'm Al Iverson and I'm here to help. You've got questions about email deliverability? Find answers here! This is where I've been writing about email technology, sender requirements and best practices, email authentication, stopping spam, and more, for twenty-four years. And if you can't find an answer in one of the 1700+ articles here, drop me a line with your question, and I'll try my best to follow up. And don't forget to subscribe to my email newsletter, so that you'll get updated info pushed to your inbox weekly.
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Weird DKIM failures? Check your header lengths

Weird DKIM failures? Check your header lengths

If you’re running into issues with DKIM signatures failing when sending to Microsoft domains, but working fine elsewhere, one thing to check is that your various email headers aren’t too long or wrapped improperly. Postmark’s blog post from January touches on this very issue ; ActiveCampaign’s Postmark platform previously generated list-unsubscribe headers that were quite long; so long as to cause a specific issue with DKIM email authentication at Microsoft. Did the sending email platform violate …

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The Latest Deliverability News

Weird DKIM failures? Check your header lengths

If you’re running into issues with DKIM signatures failing when sending to Microsoft domains, but working fine elsewhere, one thing to check is that your various email headers aren’t too long or wrapped improperly. Postmark’s blog post from January touches on this very issue ; …

Interview with Sam Masiello

It was a pleasure to sit down for a special edition of the Valimail “Ask Al” video series for a Q&A with an old friend and industry veteran, Sam Masiello. Sam and I go way back to the early days of anti-spam and email security, but his career has since evolved into a securi…

Relief for marketers? Washington email law amended

If you've been following the legal landscape for email marketing, you're likely aware of the "litigation gold rush" happening in Washington State. Thanks to a strict interpretation of the Washington Commercial Electronic Mail Act (CEMA), even the smallest tec…

When Gmail broke the rules: What a two-day glitch taught us about user intent

Steven Lunniss, Director of Deliverability for email marketing provider Cordial, was able to answer a very important question back in January, thanks to an unexpected glitch. The question: What happens to engagement and subscriber sentiment when your email messages are unexpect…

Industry: Apple to enter B2B mailbox space, Amazon exits

Here’s a quick update on recent comings and goings in the business mailbox provider space. Amazon to wind down Workmail offering Amazon just announced that they are shutting down their corporate mailbox solution Workmail. The service officially ends just about a year from now,…

DELIVTERMS: Hashbusting

It is time to clarify another technical concept here on Spam Resource, in our series DELIVTERMS, where we decode email and related acronyms and terms, helping you better understand the messaging ecosystem that surrounds you. Today, the word we’re defining is: hashbusting . If y…

Dan Stevens: Why I Built a Flat-Rate ESP in 2026

My friend Dan Stevens (who founded email verification platform Kickbox and hired me there once upon a time) has rejoined the email community! After seeing him announce unMTA , I invited him to author a guest post here to share thoughts about his new venture and what his goals …

Choosing the Right Subdomain

What happens if you choose the wrong subdomain? Does everything explode and the submarine sinks to the bottom of the ocean? Not really, but there are indeed some considerations around choice of subdomain for your various types of email messages. I recently tackled this topic in…

Podcast Fun: 175 Years of Email Experience (and counting)

I recently sat down with a bunch of new friends to sit for a podcast recording. The podcast, Email’s Not Dead , is “about how we communicate with each other and the broader world through modern technologies.” Joining me on this adventure? Jonathan Torres, Eric Trinidad, Thomas …

Cool Tool: Sender Audit by Simon Bressier

Looking for an easy way to validate that your email is configured correctly? While technical compliance is only part of the deliverability equation (don’t forget our old friends reputation and engagement), it’s still very, very important to make sure you get it right: DNS confi…

Meet Jason Morrow, Senior Email Designer & Developer

Hey, you! Are you looking for work? It’s rough out there, I know. I want to help, if I can. Every now-and-then I’m going to share a post that highlights the name and focus areas of a smart expert in the email space who is looking for work. My goal is to assist with a bit of ext…

Friday Fun: Clint Eastwood by Gorillaz

Well, since this song was originally released (in 2001) the future has indeed been movin' on. I don't know that I have any sunshine in a bag, but even lacking that, it was still great fun to see Gorillaz on SNL last week, and I rather enjoyed this little bit of time tr…

Fun with Gmail Tabs via IMAP

Like Gmail tabs? Want their categories to trickle down into your email client, if you’re not using Gmail's email client? Do you ever wish that the categories would show up as IMAP folders in Thunderbird? If you’ve answered yes to any of these questions, this clever hack mig…

Litmus Live Recap: Where are we headed in 2026?

I had a lot of fun joining Validity's Guy Hanson and Danielle Gallant recently, in our Litmus Live session, where we spoke to the topic of where email marketing is headed in 2026. And we covered a lot in that 30 minutes: deliverability trends, AI in the inbox, the future o…

Yahoo Mail: Reducing storage?

Back in September 2025, I posted about receiving notice from Yahoo that they were apparently reducing the amount of space granted to Yahoo Mail user mailboxes from 1 terabyte to 20 gigabytes. (In hindsight, I now realize that this specific new limit might be US-specific.) Whil…

Is email broken right now?

January and February were not kind to many email senders and mailbox providers. Glitches were to be found and experienced. Google accidentally misclassified a bunch of emails at one point. Yahoo and Apple seemed to be accidentally rejecting non-spam messages for a time. And Mi…

Yahoo: New sending IP ranges

Yahoo has added new, additional sending IP addresses for their outbound email, as they recently announced on the Mailop list and elsewhere. Head on over to the “ Outbound Mail Servers” page on the Yahoo Sender Hub , or pick apart their SPF record , to find the most up-to-date…

Dead domain: goo.jp

If you're sending mail to subscribers in Japan, you need to know that the Goo mail service is no more. Goo has been around rather a long time. Owned by NTT Docomo, it has existed in some form or another since May 1999 , though I'm not exactly sure when email service was…

The state of DMARC in 2026

Are you curious about the current state of DMARC in 2026? Want to learn more about the adoption of email authentication and domain protection, who out there are putting their best foot forward to prevent phishing and spoofing of their important email domains? It's something…

Microsoft rate limiting issues?

Seeing rate limiting deferrals at Microsoft OLC (Outlook Consumer/Hotmail) domains ? Specifically with this error message: 451 4.7.650 The mail server [IP Address] has been temporarily rate limited due to IP reputation. For e-mail delivery information, see https://aka.ms/postma…

Microsoft SNDS: It's alive!

Look what I just found in my email. It's an email from staff AT hotmail.com: You are receiving this message because your sender IPs are enrolled in the Junk Mail Reporting Program (JMRP). We are modernizing JMRP by rebuilding the service on a new platform. Going forward, pr…

FUD: CAN-SPAM and PO boxes

I saw somebody recently say that one of their biggest fears about starting a newsletter is that CAN-SPAM (the US federal anti-spam law) requires that you have an address in the footer and that it has to be legit, else you can (supposedly) get hit with a $50,000 fine. And also …

Newsletter Spotlight: San Diego Meteor

We’re starting a new feature here on Spam Resource: The Newsletter Spotlight! I’m a big fan of newsletters — they’re one of the best things about email — and I thought it would be fun to every so often highlight a newsletter that I’ve heard about, stumbled upon, actually subscr…

Fun with data: BIMI records in DNS (February 2026 Update)

Here’s a long overdue updated snapshot of BIMI sender logo DNS records as found in the top ten million domains data set (the domain list from host.io , where I query and log a bunch of DNS records for every domain, every month). By adjusting the view on my Wombatmail BIMI data…

Spam Resource Spotlight: Josh Nelson

Josh Nelson is the CEO of Civic Shout , an ad platform built to help progressive causes reach supporters who actually want to hear from them. Earlier in his career, Josh ran major email and digital programs for groups like Al Gore’s Alliance for Climate Protection and CREDO Mo…