Email Deliverability: Best Practices & How to Improve It

Your email marketing may not be delivering a return on your investment and time, and you may

not even be aware that it's because your messages simply aren't reaching the “Inbox.”

That sounds obvious, yet many businesses struggle with deliverability without realizing it. Their email service provider reports that campaigns were sent successfully, bounce rates remain low, and there are no obvious technical issues. Meanwhile, engagement declines and conversions suffer because more emails are landing in spam folders, promotions tabs, or being filtered before recipients ever see them.

In fact, email deliverability is constantly changing, as providers analyze each of your emails individually, checking your domain’s reputation, infrastructure, and recipient activity. A problem in any of these areas can gradually destroy the trust you’ve built up over a long period of time.

The upside is that improving it is absolutely possible and requires following proven best practices that help mailbox providers recognize you as a trustworthy sender. Let’s break them down.

Email Deliverability by the Numbers

Deliverability remains one of the biggest challenges in email marketing. Based on GlockApps' analysis of inbox placement tests conducted by real users over the past year, the average inbox placement rate across major mailbox providers rarely exceeded 60%. That means almost half of the sent campaigns are never seen.

Take a detailed look at indicators for the most popular ISPs:

GlockApps Email Deliverability Statistics 2025: Average Rates per Inbox Providers

These results highlight an important point: that even legitimate marketing emails don't consistently reach the inbox. Every mailbox provider evaluates senders differently, using its own combination of checks. As a result, the same campaign can perform very differently depending on where it's delivered.

“One of the biggest misconceptions about email marketing is that once you've had a successful campaign, future results are guaranteed. In practice, deliverability is constantly changing. Your audience and sending infrastructure evolve, mailbox providers update their filtering methods, and engagement shifts, affecting where your emails land.

Don't wait for declining performance to investigate the problem. Test your campaigns before sending, monitor authentication and sender reputation regularly to achieve good results from your email marketing constantly.” — Julia Gulevich, Head of Customer Success at GlockApps and DMARKOFF, email deliverability expert with 16+ years in email marketing.

How to Improve Your Email Deliverability: Best Practices

Improving email deliverability includes both technical and marketing efforts. Here are a few of the best practices to adopt:

1.   Build a Strong Technical Foundation.

Strong deliverability starts long before you create your first email campaign. The technical foundation behind your domain tells mailbox providers whether they can trust your emails.

Authenticate every email you send

Authentication is the first step in proving that emails sent from your domain are legitimate and haven't been forged by attackers.

Three authentication standards form the foundation of modern email security:

–        SPF verifies which servers are allowed to send emails for your domain.

–        DKIM uses digital signatures to confirm that messages haven't been altered during delivery.

–        DMARC builds on SPF and DKIM by instructing mailbox providers on how to handle emails that fail authentication and by providing valuable reporting.

These records shouldn't be checked every time you introduce a new CRM, marketing platform, help desk, or transactional email service to ensure everything remains accurate.

Monitor your DMARC reports

Publishing a DMARC record is only the first step. The real value comes from understanding what the reports reveal about your domain.

Many organizations only begin reviewing DMARC reports after experiencing spoofing attempts or deliverability issues. Monitoring them proactively helps identify problems before they affect customers or sender reputation.

DMARC monitoring can help you discover:

–        unauthorized services sending emails on your behalf;

–        outdated platforms that still appear in your DNS records;

–        authentication failures affecting legitimate emails;

–        opportunities to strengthen your domain's protection.

The challenge is that DMARC reports are delivered as XML files, making them difficult to interpret without specialized tools.

DMARKOFF simplifies this process by converting complex DMARC reports into intuitive dashboards, visual analytics, and actionable recommendations, allowing you to quickly identify authentication issues, monitor legitimate sending sources, and strengthen domain security.

2.   Maintain a Healthy Sender Reputation.

Sender reputation is built on your sending behavior and your audience's reaction to your emails. Every campaign contributes to it. High complaint rates, hard bounces, and prolonged inactivity gradually reduce trust, while consistent engagement strengthens it.

Email providers often favor senders who regularly deliver relevant content to their engaged recipients.

Keep your email list clean

One of the most common mistakes businesses make is continuing to email subscribers who stopped engaging months or even years ago.

Inactive recipients reduce overall engagement and send negative signals to mailbox providers. Over time, this can make it harder for future campaigns to reach active subscribers as well.

Don't be afraid to remove subscribers who no longer engage. Many marketers hesitate because they don't want to shrink their database, but mailbox providers care far more about engagement quality than list size.

Good list hygiene includes:

–        removing invalid and bounced addresses;

–        segmenting inactive subscribers;

–        running re-engagement campaigns before removing contacts;

–        using double opt-in whenever possible;

–        avoiding purchased or scraped email lists.

Remember that a smaller list of engaged subscribers almost always outperforms a larger list filled with inactive contacts.

Send consistently

Mailbox providers pay attention to sending behavior. For example, if you normally send a weekly newsletter, avoid suddenly sending daily promotional campaigns during seasonal sales unless you've gradually prepared your audience for the increased frequency. Likewise, sending campaigns after months of inactivity can increase the risk of filtering.

Try to maintain a predictable sending schedule. When introducing a new domain, IP address, or email platform, increase volume gradually.

3.   Focus on Recipient Engagement.

Don’t think of email deliverability as a technical configuration, because it also reflects whether recipients value your emails. Engagement begins the moment subscribers decide whether an email’s subject line seems relevant enough to click on. If your content consistently aligns with what people signed up for, engagement levels generally remain high. When expectations and content diverge, open and click-through rates typically decline.

Mailbox providers observe how people interact with messages:

–        opening them;

–        clicking links;

–        replying;

–        moving emails out of spam;

–        ignoring or deleting messages;

–        marking them as spam.

If you notice engagement declining in a specific segment, don't immediately send more campaigns. Consider reducing frequency, changing the content mix, or running a re-engagement campaign before removing inactive subscribers altogether.

These interactions help determine whether future emails deserve a place in the inbox.

Send emails your audience expects

Subscribers are far more likely to engage when emails match their interests and expectations.

Instead of sending every campaign to your entire database, segment your audience based on purchase history, preferences, or previous engagement.

Sending fewer and more relevant emails usually produces stronger engagement than increasing campaign frequency.

Monitor engagement trends

Don't evaluate campaigns solely by individual open or click rates, watch for long-term trends:

–        declining engagement;

–        increasing unsubscribe rates;

–        growing spam complaints;

–        segments that have become inactive.

These indicators often reveal deliverability problems before inbox placement begins to decline significantly.

4.   Review Your Email Content Before Sending.

Content alone won't determine inbox placement, but it contributes to the overall trust mailbox providers assign to your emails. Good email content is clear, relevant, and aligned with what subscribers expect.

ISPs evaluate the overall quality and consistency of the message, not only “spam-trigger words”. An email with a clear purpose, recognizable branding, and relevant content is much more likely to generate positive interactions than one designed only to boost sales.

Before sending, review:

–        sender name consistency;

–        visible unsubscribe link;

–        mobile responsiveness;

–        whether the subject line accurately reflects the email;

–        image-to-text balance;

–        unnecessary redirects or shortened URLs;

–        HTML rendering issues;

–        broken links;

–        readability across desktop and mobile devices.

Complicated HTML, excessive promotional language, or inconsistent branding can all affect recipient engagement, even if they don't directly trigger spam filtering.

5.   Make Deliverability Part of Your Routine.

Testing becomes even more important when introducing a new template, changing your sending infrastructure, or launching a high-value campaign. Catching a deliverability issue before sending to thousands of recipients is far easier than trying to recover afterward.

Test campaigns before launch

Even experienced email marketers can't predict exactly how every mailbox provider will treat a campaign. That's why pre-send testing has become an essential part of their workflow.

GlockApps helps test inbox placement across major mailbox providers before launching campaigns. In addition to showing where emails are likely to land, it identifies authentication issues, spam filter scores, blocklist problems, and content-related risks that could impact deliverability.

Finding problems before sending is far easier and far less expensive than trying to recover after an important campaign underperforms.

Build a continuous monitoring part of your workflow:

–        reviewing authentication records;

–        monitoring DMARC reports;

–        tracking inbox placement;

–        cleaning subscriber lists;

–        testing every new template and important campaigns;

–        maintaining consistent sending patterns.

Conclusion

Improving email deliverability is about strong authentication, healthy sender reputation, engaged subscribers, relevant content, and consistent testing.

Monitor these areas regularly and use dedicated tools like DMARKOFF and GlockApps to protect your domain and validate campaigns before sending to identify potential issues early and maximize the chances that every email reaches the audience it was intended for.