How to Test Your Emails Before Sending and Keep Them Out of Spam

Imagine spending weeks on the perfect campaign - subject lines polished, design pixel-perfect, content ready to convert. 

You hit “send” and then discover half of your emails are sitting in the spam folder. 

The good news is that you can test your emails before sending and spot issues that lead to spam folder placement. 

Here’s how to make sure your campaigns land in the inbox. 

Why Deliverability Testing Matters

Three reasons why Email Deliverability Testing matters:

• ROI Protection: If 20% of emails go to spam, that's 20% of potential revenue gone. 
• Sender Reputation: Inbox Providers track your history. One bad campaign can hurt future deliverability. 
• Engagement Impact: The more you land in inboxes, the better your opens, clicks and conversations. 

2025 Email Deliverability Checklist

1. Verify Your Authentication

Check if your SPF, DKIM, and DMARC records are set up correctly. These prove you’re the legitimate sender. 

Use MXToolbox to run a lookup. If DKIM fails, your emails may go straight to spam.

2. Add One-Click Unsubscribe

Gmail and Yahoo now require a one-click unsubscribe option. Without it, your messages may be bulked or rejected.

Your email headers should include:

List-Unsubscribe: <mailto:unsubscribe@yourdomain.com>, <https://yourdomain.com/unsubscribe>

List-Unsubscribe-Post: List-Unsubscribe=One-Click

3. Run a Spam Filter Test 

Before sending, run your emails through tools like Mail Tester or Mail Genius. These simulate ordinary spam filters. 

4. Check Blocklists

If your sending IP or domain is on a blocklist (like Spamhaus, Barracuda), many inboxes will reject your emails outright. 

5. Test Inbox Placement (Seed Testing)

Send your campaign to a seed list of test inboxes (Gmail, Yahoo, Outlook, etc.) Check whether it lands in the Inbox, Promotions, or Spam. 

6. Preview for Rendering and Accessibility

Your email should render well across all devices, modes, and accessibility standards. Use tools like HubSpot to preview before sending.

• Check Dark mode compatibility.
• Add alt text to images
• Test on mobile first
  
  

7. Strengthen Trust Signals

Custom Tracking Domain (CTD): Replace ESP default links (e.g., click.mailprovider.com) with your own branded domain. ISPs trust branded links more.

BIMI: Show your verified brand logo in inboxes. It boosts trust and can improve open rates.

What to Do If Something Fails 

Testing isn’t about perfection — it’s about prevention. If you see a red flag:

• Auth fails? Fix DNS and retest.
• Spam score too high? Edit subject line/content.
• Blocklisted? Pause sending, investigate, and delist.
• Seed test poor? Make small tweaks — subject, images, links — then retest.

After Sending, Keep Monitoring

Pre-send testing is critical, but you also need post-send visibility.

• Google Postmaster Tools: Track domain reputation and spam rates.
• Microsoft SNDS: See complaint data and trap hits.
• ESP dashboard: Monitor bounce, unsubscribe, and open rates.
  
  

Together, this tells you whether your pre-send fixes are working long-term.

Deliverability testing isn’t busywork — it’s the safety net for your marketing ROI. By running a few checks before sending, you can avoid blocklists, reduce spam scores, and land more emails in the inbox.