How to Ensure Your Emails Keep Landing in the Inbox

Email marketing is no longer a matter of simply “sending and hoping for the best.” The rules are changing, the requirements are becoming stricter, and anyone who doesn’t have their technology or data in order will notice it immediately: lower open rates, higher bounce rates, or worse — the spam folder. But what causes this? Are spam words really a risk? Is DMARC mandatory?

Within the DDMA Email Committee, we decided to put it to the test. Not with theory or slides, but by tackling a practical case to answer the question: Which factors have the most impact on email deliverability?

The assignment: help a struggling email team

We gave ourselves the following scenario:

A company sends 400,000 emails every week. But… they are experiencing deliverability issues. More and more emails are ending up in spam or are not being delivered at all. The question for the committee members: which factors are most likely having a negative impact?

In front of us were 14 cards with possible causes, from technical settings to copywriting choices. Together, we ranked them from “most impact” to “least impact.”

This exercise provided sharp insights and valuable discussions, ultimately resulting in a practical top 14 that serves as a handy checklist.

Top of the list: the must-haves

We quickly agreed on a shared number one: SPF and DKIM. You must have these properly configured; otherwise, your emails simply won’t get delivered. Due to the high sending volume, DMARC came in second place, followed by spam traps.

1. SPF and DKIM
   Without these two, your emails are at a disadvantage. SPF (Sender Policy Framework) specifies which servers are allowed to send emails on behalf of your domain. DKIM (DomainKeys Identified Mail) adds a digital signature to your emails. Both are essential for email authentication. Missing one? You risk landing directly in spam.
2. DMARC
   DMARC (Domain-based Message Authentication, Reporting & Conformance) builds on SPF and DKIM. It tells the receiving server what to do if authentication fails: block, quarantine, or still deliver the message. Without DMARC, you’re vulnerable to spoofing and have less control over your sender reputation.
3. Spam traps
   Spam traps are not real people’s addresses but addresses set up specifically to catch spammers. If you send emails to these, it signals that your list is not clean. ISPs use this to penalize senders — and rightfully so.

Middle tier: behavior and list hygiene

1. High bounce rate
   Many bounces (emails that return because an address no longer exists) damage your reputation. If your emails often don’t get delivered, providers start to doubt your reliability.
2. Inconsistent sending patterns
   A few weeks of nothing, then suddenly 400,000 emails in one day? Inbox providers like predictability. Irregular patterns can signal that something is wrong.
3. Outdated send list
   Still emailing people who haven’t opened anything in years? That’s asking for trouble. Inactive contacts mean low engagement and hurt your reputation.
4. Low interaction, few clicks
   Engagement is an important factor in reputation. The more people open and click on your emails, the better. Low interaction? Then inbox providers assume your email is unwanted.

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Bottom of the list: the refinements

1. Shared IP
   A shared IP address means your reputation can be affected by the behavior of other senders using the same IP. This doesn’t have to be a problem, but it does make you dependent on others.
2. URL shorteners
   Shortened links are sometimes used in phishing and spam. Some filters see this as suspicious. It’s better to use full, recognizable URLs.
3. Errors in HTML
   Poor or sloppy HTML code can cause your email to display incorrectly or even get blocked. Always test thoroughly before sending.
4. Missing plain text version
   Sending only an HTML version without a plain text alternative? Some systems see that as incomplete. Adding a simple text version is easy and prevents problems.
5. Low text-to-image ratio
   An email consisting mainly of images and little text is more likely to be flagged as spam. A healthy balance between visuals and text is important.
6. Spam words like “FREE”
   Long seen as a major red flag for spam filters, but now less important than previously thought. Still, filling your email with exaggerated words and exclamation marks definitely doesn’t help.

What this exercise taught us

The strength of this session lay not only in ranking the cards but especially in the discussion. By working as a team to analyze a concrete case, we quickly arrived at valuable insights:

• Many problems stem from a weak technical foundation. Start there.
• Behavior and list quality are the next logical steps. Send regularly, clean your list, and send only relevant content.
• Refinements like spam words and image ratios only make sense once the basics are in place.

In short: Deliverability is a chain. And like any chain, it’s only as strong as its weakest link.

Summary

Want to be sure your emails keep reaching the inbox? Start with SPF, DKIM, and DMARC. Then work on your sending rhythm and list quality. And always keep monitoring, because today’s rules could change tomorrow.

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