Published Monday, July 28, 2025 by Al Iverson. Click here to subscribe.

 
Happy Monday and welcome to another edition of the Spam Resource newsletter!

SMTP deferrals are a tricky topic. I write about them this week because there are a whole new generation of email marketers, developers, engineers, even platform founders, who are a bit insulated from the intracies of SMTP, thanks to to the broad proliferation of easy API-based SMTP relay/email send platforms like Amazon SES, Sendgrid, Mailgun and so forth.

You don't need to be an SMTP wizard nowadays to build a cool platform that sends good emails. And that's okay! (Though, in my opinion, deeper knowledge helps for when you run into the weird stuff.)

So what should you actually do when you run into SMTP deferrals due to a receiving mailbox provider's temporary downtime? That's the question I tried to answer in this week's featured article. I hope you find it useful!

If you're looking for other stuff to read beyond what I've shared here, I recommend reading Dan Oshinky's thoughts on why you should go download a copy of your email list today.

Last week, I asked folks, is it time to retire pre-headers, given the growth of Apple Intelligence's previews overwriting them? The feedback? Nope, not yet. Keep them. Gmail still shows them, and not everybody has a modern iPhone.

When randomly poking around in my analytics tool for the blog yesterday, I looked to see what the most read post on Spam Resource was over the past 365 days. Which one? The one where I answer the question of whether or not Comcast subscriber email addresses are at dot COM or dot NET. Spoiler: Subscribers use dot NET and it's something that I recall was confusing to so many clients back in my ESP deliverability days, to the point where we blocked comcast dot COM uploads by default, unless a client asked for it to be removed, because it was 99.9% typos meant to be dot NET. Did you ever confuse the two, as a sender or when giving out your own email address? Let me know!

And now, on to the stuff about the stuff.
 
Understanding 4xx Deferrals
Let us take a moment to talk about SMTP status codes. Specifically, the kind that start with the number 4. Say you've just sent out your latest email, whether it be a newsletter or marketing campaign. You know that it should land in the inbox right about ... now. But this time ... nothing. It's not in your Gmail, ... read more
Ziff Davis Acquires Email Industries
As reported by a press release from Ziff Davis themselves, and here on MediaPost, media publisher-slash-tech company Ziff Davis has acquired Scott Hardigree's Email Industries, a deliverability consultancy business that also includes email verification platform Alfred. read more
See you at Netroots Nation August 7
Event alert! Do you want to help make the world a better place? So do I, and I want to help keep you out of the spam folder while you do it. In New Orleans on August 7th, yours truly (Al Iverson from Valimail) will be speaking in person at Netroots Nation alongside Sandro Cocito from NGP VAN. Together, we'll unpack the current state of email ... read more
Warming Up Right: A Deep-Dive Guide from Amazon SES
Looking to migrate your email traffic to a new ESP? Or maybe you're just trying to get serious about domain and IP warming for the first time? Either way, this new warming guide from Amazon's Tyler Holmes is one of the best things I've read on the topic lately. Tyler walks you through what warming really is, why it's necessary, and ... read more
Steve Atkins: Short TTLs Causing Delivery Issues?
Some senders are reporting inconsistent, hard-to-pin-down authenticated-related delivery failures when sending to Microsoft domains. Here's a theory about on thing that might be related: overly short DNS TTL (time-to-live) settings on SPF, DKIM, or CNAME records might be ... read more
HEY: My first impressions
A bonus article from the archives (Monday, June 29, 2020)
... read more
And that's all for now! Thanks for reading.

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Mailing address: 1522 W Jarvis Ave, Chicago IL 60626. I am not a lawyer and this is not legal advice. Duh. All opinions are mine alone and do not necessarily represent the views of any group, company, organization or other person.