How to diagnose underperforming email campaigns using metrics

When an email campaign underperforms, the hardest part isn’t fixing it — it’s knowing what actually went wrong.

Low opens, weak clicks, rising bounces… each metric tells a different story. In this guide, we’ll show you how to diagnose email campaign problems using metrics, so you can take the right action instead of guessing.

Why Looking at a Single Metric Doesn’t Work

Many marketers focus on just one number — usually open rate.

The problem?
Email performance is multi-dimensional. A campaign can have:

Good opens but poor clicks
Strong clicks but high bounces
Average metrics hiding a deeper deliverability issue

To diagnose problems correctly, you need to look at how metrics relate to each other.

Step 1: Start With Open Rate (Attention & Deliverability)

Open rate answers one question:

Did people want to open this email?

If your open rate is low, common causes include:

Weak or misleading subject lines
Poor sender reputation
Inactive or low-quality lists
Deliverability issues

⚠️ If opens drop suddenly across campaigns, suspect deliverability, not content.

Step 2: Analyse Click Rate (Engagement & Intent)

Click rate shows whether readers took action.

Low clicks usually mean:

The content didn’t match the subject line
CTAs weren’t clear or compelling
The email had too many competing actions

A healthy campaign usually shows click trends moving in the same direction as opens.

Step 3: Use Click-to-Open Rate to Diagnose Content Issues

Click-to-open rate (CTOR) isolates content performance.

It answers: Once someone opened the email, did it persuade them?

High opens + low CTOR → content mismatch
Low opens + high CTOR → subject line problem, not content

CTOR is one of the fastest ways to pinpoint where the breakdown happened.

Step 4: Check Bounce Rate for List Health Problems

Bounce rate is an early warning signal.

High bounce rates often indicate:

Old or unmaintained lists
Purchased or scraped emails
Broken signup forms
Spam traps

Even a small increase in bounces can harm future deliverability.

Step 5: Watch Unsubscribe Trends (Relevance & Frequency)

Unsubscribes are normal — spikes are not.

Rising unsubscribe rates usually point to:

Sending too frequently
Content not matching signup expectations
Overly promotional campaigns

Compare unsubscribe rates across campaigns, not in isolation.

Step 6: Compare Campaigns Side-by-Side

The most useful insights come from comparison, not single reports.

Comparing campaigns helps you:

Spot gradual declines early
Identify winning formats or topics
Separate one-off failures from real trends

This is where consistent metric calculation matters most.

Turning Diagnosis Into Action

Once you identify the problem metric, your fix becomes clear:

Low opens → improve subject lines & sender reputation
Low clicks → refine content and CTAs
High bounces → clean your list
Rising unsubscribes → adjust frequency or targeting

The goal isn’t perfect numbers — it’s faster feedback loops.

Final Thoughts

Email campaigns rarely fail for one reason.

By analysing how metrics interact, you can diagnose issues quickly, make focused improvements, and avoid repeating the same mistakes.

Consistent measurement is what turns email marketing from guesswork into a system.