Introduction

When CSA approached me and invited me to write about the future of the email ecosystem and what I quickly said yes. I’m always happy to discuss email in general and deliverability in particular. The email ecosystem is changing and these changes are affecting senders of all sizes.

Deliverability professionals are particularly attuned to changes. We have to see not only the ecosystem as a whole, but we understand how changes in one area impact the whole system. We must monitor what’s happening in the technical, social, and even political arena to deliver effective results. Our insights inform business decisions in a complex and evolving environment.

I am focusing on a couple of specific areas for this post.

1. Changes and evolution of technical requirements: Large mailbox providers are increasingly filtering mail for technical standards and actively developing new standards.
2. Increased focus on user specific filtering: Consumer mailbox providers are investing in filters that provide unique inbox experiences for each user.
3. Increased integration of AI tools: Email application developers are incorporating AI tools into the inbox.

Evolution of Technical Requirements

Email, originally published by the legendary Jon Postel 1981 as the Simple Email Transfer Protocol (SMTP), has evolved over the years. Originally, the protocol was just for text email sent without much security. In the ensuing 40 years, it has been enhanced with various protocols which add functionality, security and authentication. Functional protocols include things like the MIME standard, which allows marketers to send HTML-based emails. Security protocols include things like TLS and S/MIME, which encrypt the SMTP transaction or the whole message. Authentication protocols include SPF, DKIM, and DMARC. Toghether, these protocols form the basis of modern email communication.

In recent years, there’s been a push to improve the security and trustworthiness of email. On the formal protocol end, we’ve seen the publication of a DMARCbis to refine the protocol based on more than ten years of operational experience. Another group is actively working on DKIM2. As we move into 2026, I expect to see some experimental deployments of DKIM2 code in parallel with current authentication protocols.

Beyond protocol work, major email providers like Google and Yahoo have taken steps to enhance security and trustworthiness for their own users. In 2023, they announced requirements for email senders, both large and small. In late 2025, we saw Google announce that they were stepping up enforcement of these standards with potential blocking for senders that were out of compliance. The actions inspired other major receivers to follow suit.

Technical requirements continue to evolve. As we move through 2026 and beyond, senders can expect stricter standards for email. It the past some receivers accepted mail that didn’t meet all the formal and informal requirements. This grace given to senders, particularly those sending bulk email, is ending. More mail will be rejected for technical problems. Infrastructure companies and email service providers will be responsible for much of the compliance work.

But senders cannot rely solely on vendors to meet the standards. They must monitor their vendors and insist on mail complying. Additionally, there is one standard only senders can control: complaint rate. No external entity can comply on their behalf, so keeping complaints low is their responsibility.

Improved User-Specific Filtering

Historically, reputation based spam filtering has resulted in some recipients not getting wanted mail. Early spam filtering acted on mail before it reached the inbox resulting in users sometimes finding wanted mail in their spam folder. To address this, mailbox providers started using address books to allow mail they thought might be spam to be delivered into individual user mailboxes. This was the first form of user specific filters. Over time, more effort was put into developing user specific filters to curate individual users’ inboxes.

User-specific filters are generally maintained in the email client. Most desktop and mobile clients have internal filters that react to user actions within the client. The data stays on the device and often only acts on mail when it’s viewed in that client. For instance, my desktop mail client and my mobile mail client don’t always agree about mail because I interact differently with mail in different spaces. This is personalized filtering at work. I read and interact with mail differently in each client, so each client presents mail differently based on my actions.

This personalized filtering has several impacts on the email ecosystem and how we send mail. The biggest impact for marketers is that they can’t rely on inbox testing tools as much as they could before. These tools only show how the broad, global filters deliver to a generic mailbox; they don’t capture how mail is delivered to subscribers. Some senders find some utility in the tools. In my own work, however, I only use them as one piece of data that needs to be verified and correlated with other data points before being actionable.

As we move through 2026 and beyond, I expect user specific filtering to continue to provide individualized inbox experiences. We may even get to the point where these user filters are pushed back to the SMTP transaction. So when a user marks an email as spam, future emails from that sender bounce rather than go to the spam folder. Already some providers bounce mail with a message that the recipient, not the mailbox provider, has blocked the sender. It’s important to watch how this individualized filtering affects cold outreach mail. Right now, much of the cold outreach mail is designed to avoid broad IP and domain based filters. As filtering becomes more user-specific, recipients who find value in the cold outreach can continue to receive it, but those recipients who don’t like it won’t see it.

AI in the inbox

Of course, the biggest buzz in tech is currently AI. Some companies, like Apple and Google, are trying to incorporate AI into the inbox. We have no idea how this is going to change things. Are consumers going to like the way AI curates their inbox experience? How will the AI presence in the mailbox affect how consumers interact with email? Most importantly for marketers, how is AI in the inbox going to affect how they measure performance. We’re already in a situation where non-human interactions with email affect things like open and click rates. What are the effects where there is actual AI in the inbox? The reality is none of us know the answers to these questions right now. Everything AI-related is too new to forecast the future.

The Future

As with all ecosystems, the email ecosystem has evolved over time. Right now, we’re seeing rapid changes in multiple areas. Mail has to be technically correct and meet individual mailbox provider standards in ways that wasn’t true even a few years ago. Filters are more precise and personalized than ever before. AI supporters are making a lot of promises, but it remains to be seen if those promises are ever fulfilled.

Where does that leave those of us in the email space?

Infrastructure and deliverability folks need to be on the top of their technical game. Authentication needs to be precise and accurate. Email structure needs to be compliant with all the relevant standards. Unfortunately, not everyone is there. I alerted an ESP just this month about an error in their List-Unsubscribe implementation. Multiple ESPs are discovering DKIM signing problems at Microsoft due to line length issues. Mailbox providers are expecting senders to get it right, and the consequence is undelivered mail.

Marketers need to shift their targeting from segments to individuals. As mailbox filters become hyper-personalized it’s going to be harder to manage deliverability and reach the inbox reliably without focusing on the individual. Where this is going to most affect senders, I think, is in the cold outreach space. Many recipients don’t like cold out reach at all or are simply frustrated with the amount of unwanted cold outreach. Ultra-personalized filters could result in that cold email bouncing so those recipients never have to see it.

Email is undergoing a major shift in many areas. This is both scary and exciting. The chaos and uncertainty are creating spaces for those who see the future to build new foundations and drive innovation in this critical space.