Email Marketing Metrics: Open Rate, CTR and Unsubscribes Explained

The one-minute version

Email metrics fall into three groups:

• Engagement: open rate, click rate (CTR), CTOR.
• List health and deliverability: bounce rate, unsubscribes, spam complaints.
• Business results: conversions, revenue per email, revenue per subscriber.

Opens are now the weakest signal. Make decisions on clicks and money, and keep the health metrics in check so your emails keep landing in the inbox.

Definitions and formulas

Note that email platforms calculate these slightly differently (based on sent or delivered, unique or total events). Compare numbers within the same platform.

Bounces: soft and hard

• Hard bounce: the address does not exist or the domain is permanently unreachable. Remove these addresses immediately.
• Soft bounce: a temporary issue such as a full mailbox or an unavailable server. If it repeats many times in a row, exclude the address too.

Why open rate is no longer a KPI

An open is recorded when the mail client loads an invisible tracking pixel. Apple Mail Privacy Protection (MPP) preloads email content, pixel included, through Apple's proxy servers, whether or not the person actually opened the email.

The consequences:

• open rates are inflated for Apple Mail users;
• open time and location become unreliable;
• automations triggered by "opened" fire for people who never read the email;
• subject line A/B tests judged by opens can pick a misleading winner;
• CTOR is distorted too, because opens are its denominator.

What to do: use opens only for rough trends, and test subject lines on clicks or conversions. Many email platforms can separate machine opens, so check that setting.

Which metrics to optimize for revenue

1. Conversion from email: order, lead, payment. This requires UTM tags on links plus goals in analytics or events passed to your CRM.
2. Revenue per campaign and revenue per subscriber: let you compare campaigns of different sizes.
3. Click rate: the main intermediate signal of interest.
4. CTOR: useful for judging the email itself, with an MPP caveat.

An example UTM link in an email:

https://example.com/sale?utm_source=newsletter&utm_medium=email&utm_campaign=autumn_sale

Guardrail metrics

These do not bring revenue directly, but a rise means trouble:

• Rising spam complaints: the most dangerous signal. Major mailbox providers such as Gmail and Yahoo require senders to keep complaint rates very low and publish thresholds in their sender requirements.
• Rising hard bounces: the list is outdated or contains purchased addresses.
• An unsubscribe spike: emails are too frequent or do not match what people expected when they subscribed.

How to improve the numbers

• Build your list only with explicit consent, ideally with double opt-in.
• Segment: newcomers, active buyers and dormant subscribers need different emails.
• Clean your list of inactive addresses after a re-engagement campaign.
• Set up SPF, DKIM and DMARC for the sending domain.
• Use one main call to action and a visible button.
• Make unsubscribing easy, so people do not hit "Spam" instead.

Common mistakes

• Setting goals on open rate and celebrating its growth after MPP.
• Comparing your numbers with "industry benchmarks" from random articles without knowing the method.
• Not tagging links with UTM and missing email-driven sales.
• Sending the same email to the entire list.