Email marketing metrics, defined honestly
Every email metric in one place — what it measures, what corrupts it, and which numbers deserve a place in your reporting.
Performance · 2 min read · updated
Delivery metrics
- Delivered rate. Accepted by the receiving server, as a share of sent. Note what it does not say: accepted is not inboxed — mail delivered straight to spam counts as delivered.
- Hard bounce. Permanent failure: the address does not exist. Suppress immediately and forever. Keep under 2% and treat any spike as an emergency.
- Soft bounce. Temporary failure: full mailbox, size limit, greylisting. Retried automatically; repeated soft bounces on one address eventually deserve hard-bounce treatment.
- Deferral. A 4xx "not right now" from the receiver, usually throttling. Normal in small numbers; a surge means a provider has downgraded its opinion of you.
Engagement metrics
- Open rate. Tracking-pixel loads over delivered. Structurally inflated since 2021 by Apple's pre-fetching and image proxies — usable as a trend on a fixed audience, meaningless as an absolute score, and unfit for A/B judging.
- Click-through rate (CTR). Unique clickers over delivered. The most trustworthy engagement number, lightly polluted by security scanners that click every link — prefer unique clicks and discount instant-everything clicks.
- Click-to-open rate (CTOR). Clicks over opens: content quality among those who looked. Directionally useful; its denominator inherits the open-rate inflation.
- Conversion rate. The share who did the thing the email existed for. Requires link tagging and attribution, and is the only engagement metric that connects to money.
List-health metrics
- Unsubscribe rate. Under about 0.3% per send is unremarkable. Rising unsubscribes are feedback about frequency or relevance — and they are the healthy alternative to complaints.
- Spam complaint rate. Reports over delivered. The one metric with hard provider thresholds: stay under 0.1%, never touch 0.3%. Complaints outrank every other number on this page.
- List growth and churn. Signups minus unsubscribes, bounces and suppressions. A list that only ever grows is a list that is not being cleaned.
- Revenue per send. For commerce senders, the number that ends debates the other metrics start.
Which of these belong in a report
Lead with conversions or revenue where they exist, CTR where they do not. Watch complaint rate and hard-bounce rate as guardrails with hard ceilings. Track open rate privately as a deliverability trend line, and keep it out of goals, bonuses and headlines — a target on a corrupted metric corrupts the behaviour that chases it.
Common questions
Which single metric matters most?
As a guardrail, spam complaint rate — it has hard thresholds and providers act on it directly. As a success measure, conversion or revenue per send, falling back to CTR when conversion is not measurable.
Where do benchmark numbers come from, and should I trust them?
From whichever platform's customer base published them, which is why they all disagree. Use them as sanity ranges. Your own trend on a comparable audience is the only benchmark that supports decisions.
Check your addresses now
The free InkPigeon checker runs syntax, DNS, disposable, typo and role-account analysis on any address — instantly, no signup.