Email campaign metrics: what to measure in 2025

Metrics tell you what's working in email and what isn't. But after the privacy changes, the set of "right" KPIs has shifted: what mattered in 2020 is misleading in 2025. Let's break down which metrics to measure today, with which formulas, and which values count as healthy — based on current data.

Why open rate can no longer be your north star

In September 2021, Apple launched Mail Privacy Protection: Apple Mail pre-loads the tracking pixel on delivery, so an email counts as "opened" even if no one read it. According to Litmus, by early 2025 Apple Mail accounts for around 58% of all opens, and the open-rate inflation runs 15-35% depending on the list. The takeaway: open rate is now a rough trend indicator, not a reliable metric.

Engagement metrics: what to measure

Click-through rate (CTR) is the share of recipients who clicked a link, out of emails delivered. A click requires a deliberate human action, so MPP doesn't distort it — it's a reliable signal. Formula: CTR = (clicks ÷ delivered) × 100.

Click-to-open rate (CTOR) is the share of clickers among those who opened. It shows how persuasive the email itself was. A caveat: the denominator (opens) is now polluted by MPP, so read CTOR with that in mind. Per HubSpot's 2025 analysis, at an average open rate of 38.58%, the average CTOR is 4.62%.

Outcome metrics — the ones that pay the bills

Conversion rate is the share of recipients who completed a target action (purchase, sign-up, booking). This is where an email stops being content and becomes business. It's harder to measure (conversion often happens on the site later), so attribution matters — tag your links with UTM parameters.

Revenue per Email (RPE) is the revenue attributed to email divided by emails delivered. For eCommerce and product-led businesses, this removes all the ambiguity: you can see how much money each sent email brought in. A practical tip: calculate RPE over a rolling 30-90 day window to smooth out spikes from individual campaigns.

List-health metrics — your early warning

An important nuance: a spam complaint hurts your reputation more than an unsubscribe. Someone who unsubscribes simply leaves, but someone who complains damages the deliverability of your entire list. So make unsubscribing easy (since 2024, Gmail and Yahoo require one-click unsubscribe) — that's healthier than holding on to annoyed subscribers.

How not to be fooled when metrics drop

A common mistake: open or click rates fall, and the marketer blames the subject line or content, when the real reason is that emails started landing in spam. The rule: when there's a sharp drop, check deliverability metrics first (a spike in bounces, blocks), and only then the creative. And don't use open rate as an automation trigger ("resend to those who didn't open") — because of MPP, some "non-openers" actually did open.

How often to look

Health metrics (bounces, complaints) — weekly: this is your early-warning system for deliverability problems. Revenue and trends — monthly: that filters out daily noise. Looking at the numbers daily makes little sense — it only causes anxiety over random fluctuations.

Summary

In 2025, measure what predicts outcomes: clicks (CTR), conversion, and revenue per email (RPE) as business metrics; bounces and complaints as list health. Keep open rate for comparing trends and A/B-testing subject lines, but don't base decisions on it. The right set of KPIs is the one tied to the subscriber's experience and to money — not to a tracking pixel.

Figures are drawn from Litmus, HubSpot, Klaviyo, Validity research and deliverability guidance (2024-2026). Healthy metric ranges vary by industry and campaign type.