For years, open rate was the headline number. Then Apple Mail Privacy Protection arrived, and Apple Mail started preloading email content, pixels included, whether or not a human actually read the message. Suddenly a big share of “opens” could be machines.
Opens didn’t become useless overnight, but they became unreliable as a scoreboard. If you’re still steering by open rate alone, you’re driving with a foggy windshield. Here’s what to watch instead.
The metric hierarchy
Think of your metrics as a ladder, from signals of attention up to signals of money.
- Deliverability: did it reach the inbox?
- Engagement: did people click, reply, act?
- Conversion: did they do the thing you wanted?
- Revenue: did it make money?
- List health: is the list growing and staying engaged?
The higher up the ladder, the closer to profit. Let’s go through the ones that matter.
Engagement metrics
Click rate (CTR)
The share of delivered emails that got at least one click.
Click rate = unique clickers / delivered emails x 100
This is your most reliable engagement metric today because clicks require human action (though some security scanners can produce bot clicks, which many platforms try to filter).
Click-to-open rate (CTOR)
The share of openers who clicked.
CTOR = unique clickers / unique opens x 100
CTOR used to be the go-to measure of content quality. Because MPP inflates opens, it now tends to be deflated. Still useful for comparing emails within your own list over time, especially if your platform filters machine opens. Just don’t compare it across eras or audiences.
Reply rate
Replies are gold. They signal a real relationship and are a strong positive signal for mailbox providers. Track them manually if your platform doesn’t.
Pro tip: Give every email one clear, clickable action, even if it’s just “read the full post” or “vote in this poll.” More chances to click means more reliable data about what your audience actually wants.
Conversion and revenue metrics
Conversion rate
Conversion rate = conversions / delivered emails x 100
A conversion is whatever the email was for: a purchase, a webinar registration, a download. Use UTM tags on your links so your analytics tool can attribute results to specific emails.
Revenue per email (RPE)
RPE = revenue from the campaign / delivered emails
Great for comparing campaigns of different sizes.
Revenue per subscriber (RPS)
RPS = total email revenue in a period / average list size in that period
This is the number that tells you what your list is truly worth, and how much you can afford to spend to grow it.
Profit move: Calculate your revenue per subscriber every month. If it’s rising, your content and offers are working. Then use the Email ROI Calculator to compare your email returns against your platform and content costs. That single view makes budget decisions obvious.
List health metrics
List growth rate
List growth rate = (new subscribers - unsubscribes - bounces - complaints) / starting list size x 100
This shows net growth, not just vanity signups. A list gaining lots of signups but losing just as many is running in place.
Unsubscribe rate
Unsubscribe rate = unsubscribes / delivered emails x 100
Some unsubscribes are healthy. They’re people self-selecting out instead of marking you as spam. Watch for sudden spikes after a specific email, which point to a content or frequency mismatch.
Spam complaint rate
Complaint rate = spam complaints / delivered emails x 100
This is the metric that can quietly sink everything. Gmail and Yahoo’s 2024 bulk sender requirements call for keeping spam complaint rates under 0.3%, and the widely recommended target is under 0.1%. Monitor it through your platform and, for Gmail, through Google Postmaster Tools.
Bounce rate
Bounce rate = bounced emails / sent emails x 100
Hard bounces (invalid addresses) should be suppressed automatically. A high bounce rate often points to old or poorly collected addresses.
Watch out: Complaint rate is usually calculated by mailbox providers based on mail that reached the inbox, so your platform’s number and Google Postmaster Tools’ number may differ. When in doubt, trust the stricter one and act early.
Deliverability signals to watch
- Authentication status: SPF, DKIM and DMARC passing and aligned with your sending domain.
- Domain reputation in Google Postmaster Tools, if you send enough volume to Gmail to see data.
- Inbox placement: seed tests or tools that estimate whether mail lands in inbox, promotions or spam.
- Sudden click drops across all emails: often a sign of a deliverability issue, not a content issue.
- DMARC reports: show who is sending as your domain and whether it passes.
Setting up or fixing records? Draft them with the DMARC & SPF Builder.
Your weekly metrics dashboard
Copy this into a spreadsheet. Fill it in every week, and look at the trend, not any single number.
| Metric | Formula | This week | Last week | 4-week avg | Healthy direction |
|---|---|---|---|---|---|
| Emails delivered | Sent minus bounces | Stable or up | |||
| Click rate | Unique clicks / delivered | Up | |||
| CTOR (directional) | Unique clicks / unique opens | Up | |||
| Replies | Count | Up | |||
| Conversions | Tracked via UTMs | Up | |||
| Revenue | Attributed email revenue | Up | |||
| Revenue per subscriber | Revenue / avg list size | Up | |||
| Net new subscribers | New minus all losses | Up | |||
| Unsubscribe rate | Unsubs / delivered | Stable or down | |||
| Complaint rate | Complaints / delivered | Well under 0.1% | |||
| Bounce rate | Bounces / sent | Low and stable |
A worked example
Example: Say a newsletter delivers 10,000 emails. 300 unique people click, 20 buy a product priced at $50, and 3 people mark it as spam.
- Click rate: 300 / 10,000 = 3%
- Conversion rate: 20 / 10,000 = 0.2%
- Revenue: 20 x $50 = $1,000
- Revenue per email: $1,000 / 10,000 = $0.10
- Complaint rate: 3 / 10,000 = 0.03%, comfortably under 0.1%
These are illustrative numbers, not benchmarks. Your best benchmark is your own trend line.
Metrics hygiene checklist
- Stop using open rate as your main success metric
- Filter or flag machine opens if your platform supports it
- Add UTM parameters to every link
- Track revenue per subscriber monthly
- Monitor complaint rate every send, plus Google Postmaster Tools
- Calculate net list growth, not just new signups
- Review the dashboard weekly, and act on trends
Key takeaways
- Apple MPP made opens unreliable; clicks, replies and conversions are your new scoreboard.
- Revenue per subscriber is the metric that connects email to profit.
- Measure net list growth, not just signups.
- Keep complaint rates well under 0.1%, and never near the 0.3% ceiling.
- A simple weekly dashboard beats a complicated one you never open.
Ready to see what your list is really worth? Run your numbers through the Email ROI Calculator and List Value Calculator, then join the free 7-Day Email Profit Bootcamp to start moving the metrics that pay.
Join the Profit Inbox Insiders
Weekly email marketing plays, free tools and templates. Plus the free 7-Day Email Profit Bootcamp.
