The deliverability crisis had been building for weeks. Open rates declined gradually—2% one week, another 3% the next. Nobody noticed because nobody was watching. By the time someone checked, Gmail was routing 40% of their emails to spam. Recovery took three months.
Daily metric tracking isn't about obsessing over numbers. It's about catching anomalies early, when they're still fixable. A 5% drop in open rates today is a signal. A 40% drop after weeks of ignored decline is a crisis.
These are the metrics worth checking every day.
Delivery metrics
1. Delivery rate. The percentage of emails accepted by receiving servers. This should be above 95%—ideally above 98%. A sudden drop indicates infrastructure problems, blacklisting, or authentication failures.
Delivery rate tells you emails were accepted, not that they reached the inbox. An email can be "delivered" to the spam folder. But delivery failures are immediate red flags that need investigation.
2. Bounce rate. The percentage of emails that couldn't be delivered. Hard bounces (permanent failures like invalid addresses) should be near zero if you're maintaining list hygiene. Soft bounces (temporary failures) happen but should resolve.
Track hard and soft bounces separately. Rising hard bounces suggest list quality problems. Rising soft bounces might indicate reputation issues or receiving server problems.
3. Complaint rate. The percentage of recipients who mark your email as spam. This should be below 0.1%—ideally below 0.05%. Complaint rates above 0.3% cause serious deliverability problems.
Complaints are the most damaging signal you can send to ISPs. A spike in complaints needs immediate investigation: what changed in your sending that's upsetting recipients?
Engagement metrics
4. Open rate. The percentage of delivered emails that were opened. This metric has limitations (image blocking, privacy features) but trends are meaningful. A sudden drop often indicates inbox placement problems—emails going to spam don't get opened.
Compare open rates to your baseline. A 20% open rate might be great for one sender and terrible for another. What matters is deviation from your normal.
5. Click rate. The percentage of delivered emails where recipients clicked a link. This is a stronger engagement signal than opens because it requires intentional action. Declining click rates suggest content isn't resonating or calls-to-action aren't compelling.
6. Click-to-open rate. Clicks divided by opens. This isolates content effectiveness from deliverability. If open rates drop but click-to-open stays steady, the problem is likely inbox placement. If click-to-open drops, the problem is content.
List health metrics
7. Unsubscribe rate. The percentage of recipients who unsubscribe. Some unsubscribes are healthy—people self-selecting out of content that's not for them. But rising unsubscribe rates indicate you're sending too often, content isn't valuable, or you're reaching the wrong audience.
Unsubscribes are better than complaints. Someone who unsubscribes is telling you they don't want your email. Someone who complains is telling ISPs you're a spammer.
8. List growth rate. New subscribers minus unsubscribes and bounces, as a percentage of total list size. Healthy lists grow over time. Shrinking lists indicate acquisition problems or retention issues.
A list that's shrinking faster than it's growing will eventually disappear. Track this to ensure your email program is sustainable.
Infrastructure metrics
9. Queue depth. How many emails are waiting to be sent. A growing queue indicates sending is slower than queuing—either rate limits, infrastructure problems, or volume spikes. Queues should drain, not grow.
For transactional email especially, queue depth directly affects user experience. A password reset that sits in queue for an hour is a failed password reset.
10. Send latency. Time from email request to actual send. This should be consistent and low for transactional email. Spikes indicate infrastructure problems. Gradual increases suggest capacity issues.
Setting up daily tracking
Automate metric collection. Most ESPs provide dashboards and APIs for these metrics. Pull them into a central dashboard where you can see trends at a glance.
Set thresholds for alerts. You don't need to manually check metrics if alerts notify you of anomalies. Define what "normal" looks like and alert when metrics deviate significantly.
Compare to baselines. Absolute numbers matter less than trends. A 15% open rate might be normal for your audience. What matters is whether it's changing.
Segment when investigating. Aggregate metrics hide problems. If overall delivery rate drops, segment by domain, campaign type, or recipient cohort to identify the specific issue.
What the metrics tell you
Metrics are symptoms, not diagnoses. They tell you something is wrong; investigation tells you what.
Delivery rate drops + bounce rate rises: Infrastructure or authentication problem. Check for blacklisting, SPF/DKIM failures, or server issues.
Open rate drops + delivery rate steady: Inbox placement problem. Emails are being delivered but to spam. Check reputation and content.
Click rate drops + open rate steady: Content problem. People are opening but not engaging. Review content, offers, and calls-to-action.
Complaint rate rises: Something changed that recipients don't like. Review recent campaigns, frequency changes, or list additions.
Unsubscribe rate rises: Content-audience mismatch. You're sending to people who don't want what you're sending. Review segmentation and content strategy.
Beyond daily metrics
Daily tracking catches acute problems. Weekly and monthly reviews catch gradual trends that daily noise obscures.
Weekly: Review engagement trends, list growth, and campaign performance comparisons.
Monthly: Analyze cohort behavior, long-term deliverability trends, and ROI metrics.
Quarterly: Strategic review of email program health, competitive benchmarking, and goal assessment.
The daily metrics are your early warning system. The longer-term reviews are your strategic compass.
Frequently asked questions
What tools should I use for metric tracking?
Start with your ESP's built-in analytics. For more sophisticated tracking, tools like Litmus, Validity, or custom dashboards pulling from ESP APIs provide deeper insights. Google Postmaster Tools is essential for Gmail-specific metrics.
How do I know what's 'normal' for my metrics?
Establish baselines over 4-8 weeks of consistent sending. Industry benchmarks provide rough guidance, but your specific audience and content determine your normal. Compare against yourself, not generic benchmarks.
Open rates seem unreliable. Should I still track them?
Yes, but with caveats. Apple Mail Privacy Protection and image blocking affect accuracy. Track trends rather than absolute numbers. Use click rates and other engagement metrics to supplement open rate data.
What's the most important metric to watch?
Complaint rate. It's the most damaging signal to ISPs and the clearest indicator that something is wrong with your sending. Keep it below 0.1% at all costs.