Spam Resource: All Things Deliverability
I'm Al Iverson and I'm here to help. Got questions about email deliverability? You’ve come to the right place! For 25 years, I’ve been writing about email technology, sender requirements, authentication, spam prevention, and deliverability best practices. With over 2,000 articles in the archives, there’s plenty to explore. Can't find what you're looking for? Drop me a line with your question and I'll do my best to follow up. And don't forget to subscribe to the email newsletter to get fresh deliverability insights delivered straight to your inbox every week or two.
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ISP Deliverability Guide: Comcast Xfinity

ISP Deliverability Guide: Comcast Xfinity

American multinational mass media, telecommunications, and entertainment conglomerate Comcast has somewhere north of 30 million customers with Xfinity residential broadband internet service. And while they don't publish numbers around what percentage of that subscriber base may have a comcast.net email account, it is very likely that some significant number of those customers do. Email senders, in particular US-based email marketers selling to consumers (B2C), tend to see Comcast ranked somew…

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ISP Deliverability Guide: Comcast Xfinity

American multinational mass media, telecommunications, and entertainment conglomerate Comcast has somewhere north of 30 million customers with Xfinity residential broadband internet service. And while they don't publish numbers around what percentage of that subscriber bas…

BFCM 2026: Are You Ready?

Black Friday/Cyber Monday approaches! What will this year hold in the way of deliverability challenges? When I surveyed readers last year about their biggest mailbox provider challenges during Q4, Microsoft Outlook.com took the top spot. Microsoft was clearly the biggest sourc…

Mac Users Face Microsoft 365 Sync Issues as EWS Phased Out

If you or your users rely on Apple Mail on macOS to access Microsoft 365 work or school accounts, you may soon run into unexpected sync disruptions. Starting October 1, 2026, Microsoft began disabling Exchange Web Services (EWS) by default in Exchange Online as part of a phase…

DOI vs. COI: The Pointless Word War

It's time for a trip down memory lane. We're going way back. Before "deliverability" was even a recognized industry term, our attempts to protect the inbox weren't called "email security." Instead, we called it "spam fighting." Back in …

Need Inbox Help? Ask Jen!

Looking to hire a deliverability consultant to help investigate and fix your inbox woes? J ennifer Nespola Lantz can help. She and I previously worked closely together at Kickbox, working side-by-side to provide expert deliverability services consulting, solving the tough prob…

Posta: Run Your Own Email Sending API

When you’re launching a brand new SaaS application or service, you know it’s going to send emails. That means you’ve got to pick an email delivery service. Which API are you going to use to allow your new app to send transactional emails to the world? Luckily, the market is cro…

Ask Al: What is Backscatter? (2026 Version)

I’ve written about backscatter before . (And so has USA Today .) And I’ll probably write about it again. Backscatter, at a high level, is deceptively simple. Somebody forges your domain. Somebody sends a bunch of junk email. A lot of that junk email gets rejected. Spam filters…

Dead domains (sort of): TDS Telecom offloading email service

Another regional internet service provider is getting out of the consumer mailbox hosting business. TDS Telecom has announced that it is winding down inbox hosting, handing off email duties to third-party mailbox provider Everymail . If you manage email list hygiene or delivera…

Goofus and Gallant: 3 Missed Opportunities to Do the Right Thing

Sometimes progress in email marketing best practices feels like two steps forward, one step back. Over the weekend, three emails landed in my inbox that were technically legal under US law, but pretty out of touch with modern email marketing best practices. Upon investigation, …

Dead domain: mydurango.net

If you've got email subscribers on your list from Colorado and New Mexico, take note: the mydurango.net email domain is officially dead. Ting Internet, owned by Tucows, acquired regional communication provider Cedar Networks (Zippytech) back in November 2019, and since has …

Bad Ideas: Why Giving Your Email List to a Third Party Is Just Dumb

A story recently broke on 404 Media that made deliverability experts everywhere cry a little inside: YouTube channel Channel 5 admitted to handing a CSV file of its email subscribers over to a third party so that person could market a new product to them. Putting aside the spe…

iOS27: Bringing Apple Mail Improvements

Apple will officially release iOS 27 on Monday, September 14, 2026. With that release comes an updated version of Apple Mail on mobile. 9to5Mac (and others) say that improvements will include faster message loading, more reliable search, and more. Will there be other impacts? …

New from Validity: The Heatwave Domain Blocklist

Validity just launched something very interesting: the Heatwave Domain Blocklist , and the goal is to identify and measure reputation of domains engaged in “synthetic warming” (automated exchanges between controlled mailboxes designed to make a young domain look trustworthy) an…

GPT: Let’s Talk Deliverability Analysis

Google Postmaster Tools V2, in both its user interface and API, offers information that they call a “Deliverability Analysis” (or “DeliverabilityStatusVerdict”) which attempts to provide plain language feedback and guidance on how Gmail recipients feel about your email messages…

Ask Al: GPT Transition, Reputation, and Issues

In my latest Ask Al video for Valimail , I walk viewers through the current state of Google Postmaster Tools , the very important sender feedback portal that helps to guide us all on how to maximize our chances of getting our email messages delivered to the Gmail inbox. Join me…

Mailbox full: Not always an inbox problem

When an email bounces back with a "mailbox full" or over-quota SMTP rejection, the standard assumption is that a subscriber has let thousands of unread messages pile up in their inbox. For Gmail users, that assumption might actually be wrong. As Mark Hachman points ou…

Google Resurrects Its Verified Political Sender Program

Remember Google's program to verify US political senders? (Which Jennifer Nespola Lantz covered for Spam Resource back in 2022, see here and here to revisit that bit of history.) Well, it's back. The Gmail Verified (Political) Sender Program returns, re-launching Sept…

Apple Not Changing "Hide My Email" Addresses After All

In July, I reported that Apple planned to migrate domains for both iCloud Private Relay (Sign in with Apple) and "Hide My Email" over to a new shared domain: private.icloud.com. While existing legacy addresses were set to keep working, all newly generated addresses …

Having trouble adding users and domains in GPT V2?

Multiple folks have reached out asking why they're having trouble adding new domains or users in the new Google Postmaster Tools (GPT) V2 interface. In my own testing, adding domains and users generally does work, but with a few notable quirks. The primary issue is a UI ref…