There are perhaps forty numbers on a typical email platform dashboard and eight that matter. Here they are in order, with what each tells you and where to get it.
1. Revenue or conversions per recipient
What it tells you: whether the programme works.
Why per recipient: because rate metrics improve automatically when you email fewer people, which makes them gameable. Revenue per recipient across the whole list is the only headline number that cannot be flattered by excluding people — see revenue per subscriber for the programme-level version and how to read a change in it.
Where: your platform, if it tracks conversions; otherwise your analytics with a fixed attribution window. State the window and the model every time you report it — see email attribution.
2. Spam complaint rate
What it tells you: whether the programme has a future.
Enforced from as low as 0.3% by Google and Yahoo, which is three per thousand delivered. This is the number that ends email programmes, and it is the one senders check least often because their platform usually does not show it.
Where: Google Postmaster Tools, free. Microsoft SNDS for Outlook.com.
3. Click rate on delivered
What it tells you: whether the email worked, for people who received it.
On delivered, not on opens, because the open denominator is contaminated by privacy proxies. Filter scanner clicks — those arriving within seconds of delivery, or hitting every link — particularly in B2B.
Where: your platform. Check whether it filters bot clicks before you trust it.
4. Engaged list size
What it tells you: whether you are building an audience or depleting one.
Subscribers who clicked in the last 90 days, charted over time. This single number is more informative about programme health than any campaign metric, and almost nobody tracks it, because total list size is more flattering and only goes up.
Define it on clicks rather than opens, or proxy-loaded opens will keep unengaged subscribers in your "engaged" segment indefinitely.
Where: a saved segment in your platform, recorded monthly.
5. Inbox placement rate
What it tells you: whether anyone is receiving your email at all.
Not delivery rate — those are different numbers and your platform can only measure the first. A 99% delivery rate is compatible with 40% of your mail sitting in spam. See inbox placement rate.
Where: seed testing, or domain reputation in Postmaster Tools as a free proxy.
6. Unsubscribe rate
What it tells you: whether your frequency and targeting are sustainable.
0.1–0.5% is normal. Consistently above 0.5% is a frequency or targeting problem. A very low rate deserves suspicion rather than celebration — it can mean people cannot find the link and are complaining instead. See unsubscribe rate.
Where: your platform.
7. Bounce rate
What it tells you: whether your list is clean.
Under 2%. Above that, and receiving servers start treating you as someone who does not maintain a list. Separate hard from soft — see soft bounce vs hard bounce.
Where: your platform.
8. Open rate
What it tells you: less than it used to, and it is still on the list.
Useful as a trend against your own history and, segmented by recipient domain, as an early warning for placement problems: Gmail opens falling while Outlook holds steady is a Gmail placement issue.
Not useful as an absolute figure, a benchmark comparison, or a test deciding metric.
Where: your platform, in an appendix.
The one nobody reports
Emails per conversion. Total sends divided by total conversions. It folds frequency, relevance and quality into one figure, and it is the number that tells you whether sending more is working — if you double frequency and this more than doubles, the extra volume is costing you.
Trivial to calculate, almost never on a report.
What to leave off
Click-to-open rate, because the denominator is contaminated. Deliverability rate presented as inbox placement, because it is not. Total list size as a headline, because it only rises. Individual campaign tables of twenty rows, because that is data rather than analysis.
For assembling this into something readable, see the email marketing report worth sending.
Frequently asked questions
What are the most important email marketing KPIs?
Revenue per recipient, spam complaint rate and click rate on delivered. The first tells you whether it works, the second whether it will keep working, and the third whether individual emails are landing.
Which email KPI does my platform not show me?
Spam complaint rate as mailbox providers measure it, and inbox placement. Both require Google Postmaster Tools, Microsoft SNDS or seed testing, because the filing decision happens inside the mailbox provider and is never reported back to the sender.
Should open rate still be a KPI?
As a secondary trend segmented by recipient domain, yes. As a headline or a benchmark comparison, no — privacy-protection proxy loading inflates it by an amount that varies with your audience mix.
How often should I review email KPIs?
Monthly for the full set. Campaign-level click and complaint numbers are worth a glance after each send, but most of these metrics need several campaigns before a change means anything.
