Your emails should be building trust, not disappearing into junk folders. If they’re not reaching inboxes, you’re losing engagement, wasting effort, and missing out on real business results. This guide shows you how to fix email deliverability issues fast—using smart authentication, sender reputation tactics, and email hygiene tools that actually work.
Whether you’re sending newsletters, onboarding flows, or outreach emails, this is how you land in inboxes—not spam folders.
Why Your Emails Keep Getting Flagged
You’re writing emails that matter—maybe it’s a product update, a welcome sequence, or a weekly newsletter. But if your audience never sees them, it’s like shouting into the void. Spam filters are more aggressive than ever, and even legitimate senders get caught in the crossfire.
Let’s say you run a small business and send a monthly newsletter to your customer list. You’ve got great content, but open rates are dropping. You check your analytics and notice a spike in bounces and unsubscribes. A few customers mention they found your email in their spam folder. That’s not just frustrating—it’s a signal that something’s broken in your email setup.
Here’s what might be happening behind the scenes:
- Your domain isn’t properly authenticated, so inbox providers don’t trust you.
- Your email list includes outdated or invalid addresses, which hurts your sender reputation.
- You’re sending emails too infrequently or in large bursts, which looks suspicious to spam filters.
- Your subject lines or formatting trigger spam warnings, even if your content is legit.
These issues aren’t just technical—they affect how your audience sees you. If your emails don’t show up, people assume you’re unreliable, or worse, irrelevant.
Here’s a breakdown of what spam filters look at when deciding whether to deliver your email:
| Factor | Why It Matters |
|---|---|
| Authentication (SPF, DKIM) | Verifies you’re a legitimate sender. Without it, your emails look suspicious. |
| Sender Reputation | Based on engagement, complaints, and bounce rates. Poor scores = blocked. |
| List Quality | Spam traps and invalid emails damage your credibility. |
| Content Signals | Overuse of links, images, or trigger words can flag your message. |
| Sending Behavior | Irregular volume or timing can look like spam activity. |
Even if you’re doing everything right on the content side, technical missteps can quietly sabotage your efforts. That’s why fixing deliverability isn’t just about writing better emails—it’s about making sure they actually arrive.
Here’s another example. You’re launching a new product and send a campaign to your full list. You’ve got a clean design, a strong call to action, and a great offer. But only 30% of your emails are opened. You run a test using GlockApps, and it shows that most of your emails are landing in Gmail’s Promotions tab or worse, spam. You realize you haven’t set up DMARC, and your domain reputation is low. That’s a fixable problem—but only if you know where to look.
To avoid this, you need to treat email like a system, not just a message. That means using the right tools to monitor, test, and improve your setup.
Here are three tools that help you stay out of spam folders:
- Postmark – Built for transactional emails, Postmark makes authentication easy and keeps deliverability high. It’s ideal if you send receipts, confirmations, or onboarding flows.
- Lemwarm (by Lemlist) – This tool warms up your domain by gradually increasing send volume and building trust with inbox providers. It’s especially useful if you’re starting fresh or switching platforms.
- ZeroBounce – A powerful email verification tool that removes invalid addresses, spam traps, and inactive users from your list. It’s one of the fastest ways to improve sender reputation.
If you’re serious about getting your emails seen, you need to fix deliverability first. Otherwise, you’re just sending great content into a black hole.
Authenticate Your Emails the Right Way
If your domain isn’t properly authenticated, inbox providers treat your emails like strangers knocking on the door without ID. You might be sending helpful updates or important confirmations, but without SPF, DKIM, and DMARC in place, your emails look suspicious—and suspicious emails get filtered out.
SPF (Sender Policy Framework) tells inboxes which servers are allowed to send emails on your behalf. DKIM (DomainKeys Identified Mail) adds a digital signature to prove the email hasn’t been tampered with. DMARC (Domain-based Message Authentication, Reporting & Conformance) ties it all together and gives you control over what happens when authentication fails.
Here’s how these protocols work together:
| Protocol | What It Does | Why You Need It |
|---|---|---|
| SPF | Lists authorized sending servers | Prevents spoofing and unauthorized sends |
| DKIM | Adds a cryptographic signature | Verifies message integrity and sender identity |
| DMARC | Sets policy for failed authentication | Helps protect your domain and monitor abuse |
You don’t need to be technical to set these up. Tools like Postmark walk you through the process step by step, and once configured, they keep your domain reputation clean. If you’re unsure whether your domain is properly authenticated, run a quick check using MxToolbox. It’ll show you what’s missing and how to fix it.
Authentication isn’t just a checkbox—it’s the foundation of trust. Without it, even your best emails won’t make it past the gatekeepers.
Build and Protect Your Sender Reputation
Your sender reputation is like a credit score for your email domain. If it’s low, your emails get blocked or buried. If it’s strong, inboxes welcome you in.
You build reputation by sending emails people actually want—and by avoiding behaviors that look spammy. That means keeping bounce rates low, minimizing complaints, and maintaining consistent sending patterns.
Here’s what helps:
- Send regularly, not in unpredictable bursts
- Avoid purchased or scraped email lists
- Monitor engagement—opens, clicks, replies
- Remove inactive or unengaged contacts
If you’re starting fresh or switching platforms, warming up your domain is essential. You can’t go from zero to 10,000 emails overnight. Tools like Lemwarm automate this process by gradually increasing send volume and simulating real engagement. It’s like training inboxes to trust you.
To monitor your reputation, use SenderScore.org. It gives you a score from 0 to 100 based on how inbox providers see your domain. Anything above 80 is solid. If you’re below that, it’s time to clean up your list and rethink your sending habits.
Clean Your Email List Like It’s Your Business
A messy email list is one of the fastest ways to get flagged. Spam traps, invalid addresses, and inactive users all drag down your reputation. Even if your content is great, sending to bad contacts makes you look careless.
Cleaning your list isn’t a one-time task—it’s ongoing. You should verify new signups, prune inactive users, and run full list checks every few months.
Here’s what to look for:
- Emails that bounce repeatedly
- Contacts who haven’t opened in 6+ months
- Addresses with typos or suspicious domains
- Role-based emails (info@, sales@) that often trigger filters
Tools like ZeroBounce and NeverBounce make this easy. They scan your list, flag risky addresses, and help you remove them before you hit send. If you’re using a CRM or email platform, integrate these tools directly so list hygiene becomes automatic.
Clean lists don’t just improve deliverability—they improve results. You’ll get higher open rates, better engagement, and fewer headaches.
Write Emails That Don’t Trigger Spam Filters
Spam filters don’t just look at your domain—they scan your content too. Certain words, formatting choices, and design elements can raise red flags, even if your message is legitimate.
Here’s what to avoid:
- Overuse of promotional language (free, buy now, limited time)
- ALL CAPS subject lines or excessive punctuation
- Too many links or images
- Poor HTML formatting or broken code
Instead, focus on clarity and relevance. Write subject lines that match the content. Use plain text when possible. Keep your layout clean and mobile-friendly.
Before sending, run your email through Mail-Tester or GlockApps. These tools simulate how spam filters will treat your message and give you a score. They’ll flag issues like missing headers, broken links, or risky phrases—and show you how to fix them.
You don’t need to write like a robot to avoid spam filters. Just be honest, clear, and respectful of your reader’s time.
Monitor, Test, and Improve Every Campaign
Email deliverability isn’t a set-it-and-forget-it thing. You need to monitor performance, test variations, and adjust based on what works.
Start by tracking inbox placement—not just open rates. Tools like Email on Acid and Litmus show you where your emails land (Inbox, Promotions, Spam) across different providers. This helps you spot patterns and fix issues before they escalate.
A/B testing is another must. Try different subject lines, sending times, and formats. See what gets better engagement—and use that data to refine future campaigns.
Also, pay attention to feedback loops. If users mark your emails as spam, some providers will report that back to you. Use that data to adjust your content or remove disengaged contacts.
The goal isn’t perfection—it’s progress. Every test, every tweak, every cleaned list gets you closer to consistent inbox placement.
3 Actionable Takeaways
- Set up SPF, DKIM, and DMARC today. Use Postmark or MxToolbox to make it simple.
- Clean your list with ZeroBounce or NeverBounce before your next send. It’s the fastest way to improve reputation.
- Test every email with Mail-Tester or GlockApps. Catch issues before they cost you engagement.
Top 5 FAQs About Email Deliverability
1. How often should I clean my email list? Every 2–3 months is a good rhythm. If you send frequently, monthly cleaning helps maintain reputation.
2. What’s the best way to warm up a new domain? Use Lemwarm to gradually increase volume and simulate engagement. Avoid sending large campaigns right away.
3. Can I use images and links in my emails? Yes, but sparingly. Balance visuals with plain text and avoid excessive linking.
4. What’s a good sender score? Above 80 is considered strong. Below 70 means you need to improve list quality and engagement.
5. Do I need all three: SPF, DKIM, and DMARC? Yes. They work together to verify your identity and protect your domain. Missing one weakens your setup.
Next Steps
- Run a domain check using MxToolbox or Postmark to confirm your authentication setup. Fix any gaps before your next campaign.
- Clean your email list with ZeroBounce or NeverBounce. Remove invalid addresses and spam traps to protect your sender reputation.
- Test your next email with GlockApps or Mail-Tester. Make sure it passes spam filters and lands where it should.
You don’t need to be an email expert to fix deliverability. You just need the right tools and a few smart habits. Once your emails start landing in inboxes consistently, everything else—engagement, conversions, trust—gets easier.
Start with one fix today. Whether it’s authentication, list cleaning, or testing, each step moves you closer to better results. And once you’ve got the system working, your emails will finally do what they’re meant to: connect, convert, and grow your business.