When running outbound email at scale, one of the biggest fears is this:
Are my domains burned?
Unfortunately, there’s no simple yes or no answer. The only way to know is to track the right data, consistently and at scale, per inbox and per domain.
This guide introduces the Four Horsemen metrics of deliverability (plus a few advanced extras) that the most sophisticated outbound teams are already measuring. These metrics go beyond basic setup like SPF, DKIM, and DMARC , they help you see exactly when it’s time to replace a domain or pause outbound to recover.
Track each of these over time, ideally at both the domain and inbox level:
Low reply rates can signal that your emails are landing in spam or being ignored. Look at this as a trend over time, not a one-off stat.
A warmup score tells you how “healthy” your domain and inbox are in the eyes of spam filters. Measure warmup scores over 3, 7, and 14 day windows. Use neutral copy during warmup to isolate the score from campaign content.
Run these from your actual sending tool, using your actual campaign copy. Tools like EmailGuard simulate inbox delivery and show you how often your emails reach the primary inbox, promotions tab, or spam folder.
High bounce rates (especially when segmented by domain or inbox) can indicate blocks, blacklisting, or poor list quality. Track bounce trends over time and watch for sudden spikes.
These advanced metrics help reinforce or clarify what the core four are telling you:
Blacklist Monitoring
Check if your domain or IP is listed on known blocklists (especially Spamhaus or SURBL).
Probabilistic Spam Scoring
Use content-level spam checks to predict how likely it is your copy will trigger spam filters.
Spam Filter Testing
Simulate deliveries to major email providers to see how your messages perform across real-world filtering systems.
Looking at a single metric in isolation rarely tells the full story. But when you combine all four (plus the bonus metrics), you get a high-confidence, data-backed view of your deliverability.
Here’s how to interpret patterns:
Low reply rates?
Start by checking inbox placement tests. Are your emails going to spam?
Failing placement tests?
Check warmup scores. Poor warmup performance over the last week may explain inbox issues.
High bounces?
If bounce rates have increased, it could indicate your sender reputation is declining — or your domain has been flagged.
If everything looks healthy, but you’re still not getting replies, the issue might be your offer or targeting, not deliverability.
Using tools like EmailBison and EmailGuard together, you can automate tracking of all these metrics. If you use n8n, Make, or similar tools, you can create workflows that:
Run placement tests every 3 or 7 days
Monitor bounce rates and warmup trends
Flag blacklists and spam scores
Trigger alerts or domain swaps automatically
This puts your deliverability on autopilot, and helps you stay proactive instead of reactive.
Note:
The goal is not just to recover from deliverability issues, it’s to prevent them entirely by watching for early warning signs.
