Email Deliverability in 2026: The Invisible Work That Keeps Your Emails in the Inbox

Apsis Deliverability Blog Series — Part 1 of 3

Did You Notice Anything?

In early 2026, Microsoft quietly changed their filtering rules. Without warning, a considerable share of emails sent to Microsoft-managed domains started getting blocked. Lower-volume sending IPs were unexpectedly affected, impacting automated marketing and transactional traffic more severely than high-volume bulk senders. 

For most Apsis customers? They didn't notice a thing.

That's because Jesper Sörtoft, our Deliverability Specialist, was already working behind the scenes, opening countless tickets with Microsoft, keeping the dialogue going, and pushing relentlessly until our customers' emails continued reaching their recipients. What turned out to be a miscalibrated AI filter on Microsoft's end was resolved quietly, smoothly, and without business disruption. Microsoft were slow to acknowledge the issue, but persistent escalation from Jesper eventually got things moving.

When deliverability works, you don't notice. When it doesn't, your entire business feels it.

This is the reality of email marketing in 2026: the landscape shifts constantly, ISPs update their algorithms without announcement, and what worked yesterday might not work today. Welcome to our three-part series on email deliverability in 2026. In this first instalment, we'll explore what's happening right now in the inbox ecosystem, examine the challenges facing email marketers today, and share actionable strategies to keep your emails landing where they belong. 

The Modern Deliverability Landscape: What You're Up Against

Email has never been more sophisticated, or more scrutinised. Today's inbox providers use artificial intelligence, machine learning, and complex reputation systems to determine whether your carefully crafted email reaches the inbox, lands in the promotions tab, or gets blocked entirely.

AI-Powered Filtering Is Now the Standard 

Gone are the days of simple spam filters looking for dodgy keywords and suspicious links. Modern ISPs deploy sophisticated AI systems that analyse:

• Engagement patterns over time: Not just whether emails are opened, but how quickly, on which devices, and what actions follow
• Sender behaviour consistency: Sudden volume spikes, unusual sending times, or changes in content patterns trigger immediate scrutiny
• Content authenticity indicators: AI can detect mass-generated content, template overuse, and suspicious link patterns

What this means for you: Technical compliance is table stakes. ISPs can now distinguish between emails that meet minimum standards and emails that recipients actually want. Authentication protocols and list hygiene remain essential, and the two are more closely connected than most people realise, but engagement quality is ultimately what determines whether you truly succeed.

Jesper's insight: 

"I see marketers obsessing over technical configurations whilst ignoring the fundamental question: do people actually want these emails? The most sophisticated authentication setup won't help if recipients consistently delete your messages within seconds." 

Engagement Signals Have Evolved Beyond Traditional Metrics

Open rates and click-through rates still matter, but they're increasingly unreliable as a primary signal, particularly with Apple Mail Privacy Protection masking genuine open behaviour. Modern filtering systems track far more nuanced signals:

• Read time: How long recipients spend viewing your email
• Scroll depth: Whether they're engaging with content beyond the fold
• Deletion patterns: Emails deleted unread send powerful negative signals
• Move-to-folder behaviour: Recipients organising your emails into specific folders indicates high interest
• Reply rates: Two-way conversation signals genuine relationship and trust, one good reason never to send from a no-reply address, which cuts off this signal entirely

The takeaway: Focus on creating emails people want to read, not just emails that technically reach the inbox. 

ISP Relationships: The Hidden Success Factor

Here's something most marketers don't realise: when deliverability issues arise, technology alone rarely solves them. The Microsoft incident perfectly illustrates this reality.

When Microsoft's filtering changes unexpectedly affected lower-volume IPs, there was no technical fix available to senders. Authentication was correct. Lists were clean. Content was legitimate. None of that mattered because the issue wasn't sender behaviour, it was ISP filtering logic: a miscalibrated AI system that wasn't distinguishing between legitimate senders and spammers.

The solution required direct communication with Microsoft: understanding their concerns, demonstrating sender legitimacy, and continuing to escalate until they took action.

Jesper's perspective:

 "When an issue emerges, I often know where or who to reach out to because I'm already in ongoing conversations with ISP teams—not just when problems arise. When the Microsoft situation developed, the question wasn't who to call. It was how to keep the pressure on professionally until they acknowledged the problem."

Result: Customers kept sending. Emails kept delivering. Business continued uninterrupted.

Privacy-First Features Are Now Universal

Privacy-enhancing features have proliferated across major email clients:

• Link protection services: URLs are scanned and sometimes rewritten before users click them
• Image proxy servers: Images load through intermediary servers, masking user IP addresses and behaviour
• Stricter third-party tracking policies: Embedded tracking pixels face more restrictions

These features protect user privacy, which is fundamentally positive. However, they require marketers to adapt measurement strategies and focus on engagement quality rather than vanity metrics. 

Authentication Has Become More Complex

SPF, DKIM, and DMARC are non-negotiable baselines in 2026, but ongoing monitoring matters as much as initial setup. Configurations can silently break as infrastructure evolves, and problems often go unnoticed until a major client reports delivery issues.

One addition worth considering is BIMI (Brand Indicators for Message Identification), which lets your brand logo appear next to emails in supporting inbox providers like Gmail and Yahoo. It's not a deliverability requirement, but it does act as a visual trust signal and is valued by many marketing teams. Whether it's right for your programme depends on your priorities.

The more practically impactful step is signing up for Google Postmaster Tools and Microsoft SNDS. These give you visibility into your domain's reputation and complaint rates at the ISP level, data that Apsis can't access on your behalf, and that you genuinely need to make good decisions.

Want expert deliverability support included? See what Apsis One includes →

The Microsoft Case Study: Modern Deliverability in Action

What Happened?

Starting in January 2026, Microsoft began blocking a considerable share of emails to Microsoft-managed domains (Outlook.com, Hotmail, corporate Microsoft 365 accounts). The filtering specifically targeted lower-volume sending IPs, affecting automated marketing and transactional email, precisely the types businesses depend on most. 

Why Traditional Solutions Failed

This wasn't a problem you could solve by improving authentication, cleaning lists, or adjusting content. Every traditional deliverability recommendation was already in place. The issue was a miscalibrated AI filter on Microsoft's side, one that wasn't distinguishing between legitimate lower-volume senders and spammers, and which Microsoft were initially slow to acknowledge. 

How Expertise Made the Difference

Jesper approached this as a communication and relationship challenge:

1. Rapid pattern identification: Spotted the Microsoft-specific issue within days
2. Direct ISP engagement: Created multiple support tickets and maintained constant communication
3. Evidence-based advocacy: Demonstrated Apsis's authentication protocols and legitimate customer sending behaviour
4. Persistent escalation: Maintained pressure until Microsoft acknowledged the issue and made the necessary adjustments

The result: Issue resolved. Emails flowing normally. Customers experienced zero business disruption. 

Jesper's 5 Essential Deliverability Strategies for 2026

1. Audit Your Authentication Stack Properly

Don't just verify that SPF, DKIM, and DMARC exist. Verify they're working correctly:

Use authentication testing tools to confirm proper configuration and ensure DMARC is set to at least p=quarantine and that you're actively reviewing DMARC reports, this is where real insight lives

Action: Register your domain with Google Postmaster Tools and Microsoft SNDS today if you haven't already. 

2. Practise Ruthless List Hygiene

List hygiene and engagement are two sides of the same coin, you can't manage one without the other.  

• Remove hard bounces promptly (Apsis One automates this)
• Address subscribers with 6+ months of zero engagement via re-engagement campaigns or removal
• Be aware that spam traps often follow a predictable lifecycle: an address is active, then abandoned, then deleted, and around two years later repurposed as a trap. A list you haven't sent to in a long time is a risk. Consistent sending cadence is your best protection
• Implement double opt-in to ensure genuine subscriber intent
• Monitor engagement trends to catch declining interest early

Jesper's principle: "Quality always beats quantity. Ten thousand engaged subscribers deliver better results—and better deliverability—than one hundred thousand indifferent ones." 

3. Focus on Real Engagement Metrics

Stop obsessing over open rates, particularly given how unreliable they've become.

Instead, measure:

• Click-through rates and website traffic originating from emails
• Conversion rates and revenue attribution
• Reply rates and genuine two-way conversations
• Survey responses and direct feedback 

4. Implement Adaptive Sending

Not everyone wants emails at the same frequency. Use engagement data to tailor your approach:

• Increase frequency for highly engaged subscribers who consistently interact
• Reduce frequency for moderate engagers showing declining interest
• Create win-back campaigns for subscribers at risk of disengagement
• Allow subscriber preference centres where people control their own frequency 

5. Monitor Reputation Proactively

Don't wait for deliverability problems to discover reputation issues:

• Check Google Postmaster Tools weekly
• Monitor Microsoft SNDS
• Review domain reputation status regularly, this is distinct from IP blacklist monitoring, which Apsis handles on your behalf
• Track engagement trends to catch problems whilst they're small 

The Human Element: Why Automation Isn't Enough

Modern email platforms offer impressive automation capabilities: automatic bounce handling, real-time authentication validation, predictive send-time optimisation, AI-powered subject line testing. These features are valuable and handle the routine work efficiently.

But when ISPs change their filtering rules without notice, when reputation issues require direct negotiation, or when a miscalibrated AI filter starts blocking legitimate mail, that's when human expertise becomes irreplaceable. The Microsoft incident is one example, but issues of this kind surface every week.

You're not just buying email marketing software, you're partnering with deliverability experts who work behind the scenes every single day. 

Looking Ahead: Parts 2 and 3

In Part 2, we'll explore regional compliance and privacy strategies: navigating GDPR, CASL, CAN-SPAM, and emerging regulations; regional deliverability differences across Europe, North America, APAC, and LATAM; and Jesper's insights on what really drives inbox placement across different markets.

In Part 3, we'll dive deep into advanced authentication, technical infrastructure optimisation, crisis management strategies, and Jesper's predictions for deliverability in 2027.

END OF PART 1 — Apsis Deliverability Blog Series 2026

Part 2 of 3 Coming soon →