You did a great job with the subject line. Your dynamic content is ready. Your timer is counting down. Everything looks great until your email goes to the spam folder, where no one can see it. You’ve written a great subject line. Your dynamic content is set up. Your countdown timer is ticking. Everything looks perfect… until your email lands in the spam folder and nobody sees any of it.
The silent killer of email marketing performance is poor deliverability. No matter how well-designed or personalized your emails are, they won’t get to the inbox. The good news is that you can catch most problems with deliverability before you hit send.
This is how to do it.
Why Email Deliverability Should Be Your First Check, Not Your Last
Most marketers see deliverability as a problem that comes up after open rates drop or a big campaign doesn’t do well. But by that time, the damage has already been done.
Email services like Gmail, Outlook, and Apple Mail use a number of signals to figure out where your email should go. These include the reputation of the sender, the authentication setup for the domain, and the content of the email itself. No matter how clean your list is or how active your subscribers are, any of these can send you to the spam folder. Inbox providers like Gmail, Outlook, and Apple Mail use a combination of signals to decide where your email goes: your sender reputation, your domain authentication setup, and the content of the email itself. Any one of these can send you to the spam folder, regardless of how good your list hygiene is or how engaged your subscribers usually are.
The two most common reasons why deliveries fail are the following:
- Authentication misconfiguration means that your SPF, DKIM, or DMARC records are broken, missing, or not in the right place. This tells inbox providers that they can’t be sure you are who you say you are.
- High spam content score: Your email’s subject line, body, or formatting is causing spam filters to block it before a person even sees it.
You can fix both of these problems, but only if you catch them first.
Step 1: Test Your Email Authentication Setup
Your sender reputation is based on how well you authenticate your domain. Even a well-written email to a clean list can end up in spam without it.
The three things every email sender should keep: Your domain authentication is the foundation of your sender reputation. Without it, even a perfectly written email to a pristine list can end up in spam.
The three records every email sender needs:
- SPF (Sender Policy Framework) tells email providers which mail servers are allowed to send email from your domain.
- DKIM (DomainKeys Identified Mail) adds a cryptographic signature to your emails so that service providers can check that they haven’t been changed while they were being sent.
- DMARC (Domain-based Message Authentication, Reporting & Conformance) connects SPF and DKIM and tells email providers what to do when an email doesn’t pass authentication checks.
You might not think it, but missing or misconfigured records happen more often than you think, especially after changing domains, ESPs, or adding new sending tools to your stack.
Use Alterable’s free Email Deliverability test to check your setup in seconds. Enter your domain and the tool will instantly check your MX, SPF, DKIM, and DMARC records, flag any issues, and tell you exactly what to fix. No signup required.
Step 2: Check Your Email Content for Spam Triggers
Authentication lets you in, but your content still has to get through the filter. Authentication gets you through the door, but your content still has to pass the filter.
Spam filters use hundreds of rules to rate the content of your emails. If you use too many words like “FREE” or “GUARANTEED” in all caps, have a lot of images compared to text, don’t have any unsubscribe links, or use certain HTML formatting patterns, your spam score could go above the level that inbox providers use to send you to junk.
SpamAssassin is the standard tool that most ESPs and inbox providers use behind the scenes. It is an open-source spam filter that gives your email content a score. The lower the score, the better. In general:
- 0–2: You’re in good shape
- 2–5: Worth reviewing, some filters may flag this
- 5+: High risk of landing in spam
Use Alterable’s free Content Spam Checker to test your email copy before you send. Paste your content in, run the check, and get an instant SpamAssassin score with a breakdown of exactly which rules you’re triggering and why. Fix the issues it flags, re-test, and send with confidence.
Step 3: Run Both Checks Together Before Every Campaign
Each check alone doesn’t tell the whole story. Your content can hurt your deliverability even if your authentication is perfect, and the other way around. The easiest way to protect every campaign is to include both checks on your pre-send checklist.
A practical pre-send workflow:
- Finalize your email copy in your ESP.
- Copy the HTML or plain text and run it through the Content Spam Checker. Fix any rules firing at high severity.
- Run the Email Deliverability Test on your sending domain. Confirm SPF, DKIM, and DMARC are all passing.
- Send a test to a seed address or inbox testing tool.
- Send your campaign.
This might add five minutes to your work. It would take a lot longer to fix a deliverability problem, or worse, to send again to a list that wasn’t interested.
Common Fixes for Failing Deliverability Tests
SPF not found or failing: Your SPF record needs to be published as a TXT record in your DNS. Most ESPs provide the exact record you need to add. If you’ve recently added a new sending tool, make sure it’s included in your existing SPF record — you can only have one.
DKIM missing: Your ESP should provide a DKIM key to add to your DNS. This is usually a CNAME or TXT record. After adding it, allow up to 48 hours for DNS propagation before testing again.
No DMARC record: Even a minimal DMARC policy (v=DMARC1; p=none; rua=mailto:[email protected]) is better than no DMARC at all. It signals to inbox providers that you’re monitoring your domain and puts you on the path to a stricter policy over time.
High spam score: Look at the specific rules the checker flags. Common culprits include subject lines with too many capital letters or exclamation marks, missing plain text versions, a high link density, or using a free sending domain (like Gmail or Yahoo) instead of your own.
The Bottom Line
It doesn’t matter how good an email is if it’s in the spam folder. You only need to do two quick checks (one on your content and one on your authentication) to make sure your campaigns get to the right place.
Both tools are free, require no account, and take less than a minute to run:
Make them part of your pre-send checklist and you’ll spend a lot less time wondering why your open rates dropped.
Alterable helps email marketers add real-time personalized content to their campaigns — countdown timers, dynamic products, location-based images, and more.
