Most email teams track the same three metrics: open rate, click rate, and unsubscribe rate. These are useful. They are not sufficient.
Open rate is inflated by Apple Mail Privacy Protection. Click rate is real but does not distinguish between a delivered inbox email and a clicked spam-folder email. Unsubscribe rate misses the people who stop engaging without formally unsubscribing.
None of these metrics tell you whether your programme is healthy in the way that determines long-term deliverability and revenue performance. This guide introduces the metrics that do the ones that measure programme health rather than campaign performance, deliverability rather than engagement, and trends rather than snapshots.
The Problem with Standard Email Metrics
Open rate, click rate, and unsubscribe rate measure what happened with the emails that were sent. They do not tell you the health of the infrastructure that sends them or the trajectory of the programme over time.
Consider a programme with stable 25% open rates and 3% click rates. Everything looks fine. But if domain reputation has moved from High to Medium over the past 90 days, those metrics will be declining in the next 60 to 90 days as fewer emails reach the inbox. The standard metrics do not warn you. The programme health metrics would have warned you weeks ago.
Additionally, Apple Mail Privacy Protection (MPP) has fundamentally compromised open rate as a reliable metric. For programmes with significant Apple Mail audiences, measured open rate may be 20 to 35 percentage points higher than genuine human open rate. A “25% open rate” may represent 8 to 12% genuine opens, with the remainder generated by Apple’s preloading proxy servers.
The standard metric set is broken in this dimension and does not have a clear replacement within the standard dashboard.
Domain Reputation Score: The Most Important Metric You Are Not Tracking
Domain reputation at Gmail visible in Google Postmaster Tools is the single most predictive indicator of future email performance. It predicts inbox placement before inbox placement changes. It predicts open rate changes before open rates change.
The metric is simple: High, Medium, Low, or Bad. Check it weekly.
Why it is the most important metric:
Changes in domain reputation precede changes in campaign performance by weeks. When reputation moves from High to Medium, inbox placement is already declining for some contacts. When inbox placement declines, open rates follow. When open rates follow, click rates follow. By the time open rate is visibly declining, the reputation problem has been building for 2 to 4 weeks.
Monitoring domain reputation weekly means you catch the problem when it first appears at the reputation level rather than 4 to 6 weeks later when it appears in campaign metrics.
How to track it:
Register your sending domain in Postmaster Tools at postmaster.google.com. Check the Domain Reputation chart weekly. Record the status each week in a simple spreadsheet with date and status (High/Medium/Low/Bad) to give you a trend history.
Inbox Placement Rate: What Actually Determines Reach
Inbox placement rate is the percentage of delivered emails that reach the inbox as opposed to spam or Promotions.
Your delivery rate tells you what proportion of emails were accepted by the receiving server. Your inbox placement rate tells you what proportion actually reached the inbox. These numbers can be vastly different.
Most programmes do not measure inbox placement rate because it requires seed list testing, sending to test addresses at major providers,s and checking where the email lands. This is an additional step and cost compared to relying on ESP metrics.
But inbox placement rate is the metric that most directly determines how many subscribers actually see each campaign. A programme with 90% inbox placement is fundamentally different from one with 60% inbox placement, even if both show identical delivery rates.
How to measure it:
Use a seed list testing service such as GlockApps. Send each campaign to their seed list before or alongside the main campaign send. Review the placement results. Track inbox placement rate over time alongside domain reputation.
Target: above 90% at Gmail and Outlook. Below 80% at either major provider requires investigation.
Hard Bounce Rate Trend: The List Quality Indicator
Hard bounce rate per campaign is a standard metric. The trend in hard bounce rate over time is a more powerful indicator that most programmes do not explicitly track.
A programme with consistent 0.3% hard bounce rates across 20 campaigns has healthy list quality management. A programme where hard bounce rate trends from 0.2% to 0.3% to 0.5% to 0.8% over six months has a list quality problem that is worsening and will eventually cross thresholds that affect domain reputation.
Why the trend matters more than any single number:
A single campaign with 1.2% hard bounces might be caused by a specific bad import. If the next campaign returns to 0.3%, the issue was contained. If bounce rate never returns below 0.8%, the problem is structural: ongoing acquisition of invalid addresses or insufficient verification cadence.
How to track it:
Pull hard bounce rate from every campaign in the past 12 months. Plot it over time. Is the trend flat, declining (good), or rising (concerning)? A rising trend requires investigating: which acquisition sources are producing the highest invalid rates? When was the full list last verified?
Complaint Rate: The Reputation Killer Most Teams Ignore
Spam complaint rate is the most damaging metric to domain reputation, and the one most programmes track least carefully.
Gmail’s threshold for filtering action isa 0.10% spam rate in Postmaster Tools. Most programmes do not know what their Gmail spam rate is because they rely on their ESP’s complaint rate, which does not include Gmail feedback (Gmail has no feedback loop programme).
The Gmail Postmaster Tools spam rate is the authoritative complaint rate for Gmail. It is separate from your ESP’s complaint data and typically shows higher rates because it captures Gmail-specific complaint behaviour.
How to track complaint rate:
Two sources together give a complete picture.
Source 1: Your ESP’s complaint rate. This reflects complaints from Yahoo, Microsoft, and other providers with feedback loops.
Source 2: Google Postmaster Tools spam rate. This reflects Gmail complaints.
Check both weekly. Track both over time. If Postmaster spam rate is above 0.08% consistently, investigate the campaigns and segments generating the highest complaints.
Click-to-Open Rate vs Overall Open Rate
Click-to-open rate (CTOR) measures clicks as a percentage of opens. It reflects content quality among those who opened.
Why CTOR is more reliable than open rate:
CTOR eliminates the MPP inflation problem. Apple’s proxy servers load tracking pixels (generating open events) but do not click on links. A click that Apple’s server makes on the tracking pixel from preloading does not generate a click event; only a genuine human click does.
CTOR therefore reflects a population of genuine human openers rather than all apparent opens. For programmes with significant Apple Mail audiences, CTOR is a more reliable engagement signal than either open rate or click rate alone.
How to track CTOR:
Most ESP dashboards show CTOR alongside open and click rate. If not, calculate it: clicks ÷ opens = CTOR.
A declining CTOR over time suggests content quality problems or relevance drift; FT openers are reading your subject lines but finding the email body underwhelming relative to their expectation. A stable or rising CTOR suggests content is well-aligned with subscriber expectations.
List Growth Rate Net of Churn
Raw list growth (new subscribers per month) is a commonly tracked metric. Net list growth new subscribers minus unsubscribes, bounces, and suppressions is a more honest picture.
A programme adding 1,000 new subscribers per month but losing 800 through churn has net growth of 200. A programme adding 500 new subscribers and losing 50 through churn has net growth of 450, half the gross growth but more than double the net.
Why net growth matters for programme health:
Net negative list growth, losing more contacts than you acquire,e indicates a programme that is consuming its audience faster than it is building it. This is sustainable for a finite period. Eventually, the programme is primarily sending to a disengaged, low-quality, shrinking audience.
Net positive growth with a high gross growth rate combined with a high churn rate indicates acquisition quality problems. You are acquiring contacts who leave quickly because the list-joining experience does not match the email experience.
How to track it:
Monthly: new contacts added minus contacts suppressed (from bounces, unsubscribes, and verification-driven suppressions). This is your net list growth. Track it alongside gross growth and your suppression breakdown (how many suppressions were bounces, unsubscribes, or verification-driven).
Revenue Per Email Sent
Revenue per email sent (or revenue per email delivered) is the ultimate business health metric for commercial email programmes.
It integrates deliverability (inbox placement affects opens), engagement (opens affect clicks), and conversion (clicks affect revenue) into a single number that reflects the combined output of all programme elements.
A programme with declining inbox placement, declining open rates, and declining click rates shows this trend first in revenue per email sent. Conversely, a programme that improves deliverability without changing content often sees immediate revenue per email improvements because the same content now reaches more inboxes.
How to track it:
Total email-attributed revenue in a period ÷ total emails sent in that period = revenue per email sent.
This requires revenue attribution from your ESP or attribution analytics. Many ESPs offer revenue tracking through direct integration with e-commerce platforms (Klaviyo and Shopify, for example, have native revenue tracking).
Building a Programme Health Dashboard
A programme health dashboard aggregates these metrics into a weekly view that tells you whether your programme is improving, stable, or declining.
Weekly metrics to track:
- Domain reputation (High/Medium/Low/Bad from Postmaster Tools)
- Postmaster Tools spam rate (%)
- Hard bounce rate from most recent campaign (%)
- Inbox placement rate (if a seed list test was run this week)
Monthly metrics to track:
- Hard bounce rate trend over 3 months (charted)
- Complaint rate trend from ESP and Postmaster Tools over 3 months (charted)
- CTOR trend over 3 months (charted)
- Net list growth (subscribers added minus suppressions)
- Revenue per email sent (for commercial programmes)
A simple spreadsheet with date columns and these metric rows provides a programme health trend view that campaign-level metrics cannot. When one metric moves, it often signals what will move next, giving you a warning to investigate and act before the impact reaches campaign performance.
Key Takeaways
- Standard metrics (open rate, click rate, unsubscribe rate) measure campaign performance. Programme health requires additional metrics that measure infrastructure and trends.
- Domain reputation in Postmaster Tools is the most predictive indicator. It shows reputation changes 4 to 6 weeks before they appear in campaign open and click rate data.
- Inbox placement rate requires seed list testing to measure accurately. It directly determines what proportion of your audience actually sees each campaign. Delivery rate does not measure this.
- Track hard bounce rate as a trend over time, not just per campaign. A rising trend over three months indicates a worsening list quality problem regardless of any single campaign’s acceptable number.
- Gmail spam rate in Postmaster Tools is the authoritative complaint metric for Gmail. Your ESP’s complaint rate does not include Gmail feedback.
- CTOR (click-to-open rate) eliminates Apple MPP inflation and provides a more reliable content engagement signal than either open rate or click rate alone.
- Revenue per email sent integrates deliverability, engagement, and conversion into a single business health indicator. A rising revenue per email metric validates improvements across all programme dimensions.
Frequently Asked Questions
Review domain reputation and spam rates weekly. Check bounce, complaint, engagement, and revenue trends monthly, with a full programme review each quarter.
Check both your conversion funnel and inbox placement. Stable opens can sometimes hide declining inbox reach due to factors such as Apple MPP or Promotions-tab placement.
Use donation conversion rate or volunteer action rate per email sent. Choose the outcome that best reflects your organisation’s goals.
No single metric tells the full story. Monitor reputation, complaints, bounces, engagement, inbox placement, and the business outcome together.
Watch for rising complaints or bounces, declining engagement, reputation changes, and unexplained drops in conversions. Regular trend reviews help catch issues early.
Conclusion
The standard email metric set was designed to measure campaign performance. It does not measure programme health. The metrics that predict programme health domain reputation, inbox placement rate, hard bounce rate trend, complaint rate, and revenue per email require different data sources and a different tracking cadence.
Build the programme health dashboard. Check it weekly for the fast-moving metrics and monthly for the trend metrics. The patterns these metrics reveal will tell you more about your programme’s trajectory than any campaign-level analysis.
