Open rate is the percentage of email recipients who opened a specific email campaign. It’s calculated by dividing the number of unique email opens by the number of emails successfully delivered, then multiplying by 100. For decades, open rate was treated as the primary email marketing performance metric — a proxy for subscriber engagement and content relevance. That picture changed significantly in 2021.

Apple’s Mail Privacy Protection (MPP), introduced with iOS 15 in September 2021, fundamentally altered how open rates should be interpreted. MPP preloads email tracking pixels on Apple’s proxy servers, registering an “open” even when the subscriber never actually views the email. For businesses with a significant portion of their list using Apple Mail (which is common, given iPhone’s market share), open rates are now meaningfully inflated and unreliable as a standalone metric. Understanding this context is essential to interpreting open rate data honestly.

How Open Rate Is Calculated — and What’s Changed

Traditional open rate:
(Unique opens ÷ Emails delivered) × 100

A 1,000-person list that delivers 980 emails and records 250 opens has a 25.5% open rate.

The Apple MPP problem:
Apple’s MPP processes emails through proxy servers that fire tracking pixels automatically when Apple Mail fetches content — before the subscriber reads anything. The result: if 40% of your list uses Apple Mail and has MPP enabled (opt-in, but heavily adopted), your open rate may reflect automatic proxy opens, not real human opens.

Industry data shows open rates spiked immediately after the MPP rollout. A newsletter averaging 28% opens before iOS 15 might show 45–55% post-rollout — not because more people are reading, but because Apple’s servers are registering opens on behalf of subscribers.

What this means in practice:
– Open rate is still worth tracking for trend analysis, but not as an absolute engagement signal
– Comparative open rates (one campaign vs. another) remain somewhat useful if your audience mix is consistent
– Click-through rate (CTR) has become the more reliable primary engagement metric
– Retention metrics, conversion rates from email, and reply rates provide more accurate signals of genuine engagement

Purpose & Benefits of Tracking Open Rate

1. Gauge List Health and Subject Line Effectiveness

Even with MPP inflation, open rate provides relative performance data. If one subject line consistently produces higher open rates than another in your A/B tests, that signal is meaningful — both results are affected equally by MPP, so the relative difference reflects actual subject line impact. Subject line testing remains valuable; the absolute percentages are just less trustworthy than they used to be.

2. Identify Deliverability Issues

A sudden, unexplained drop in open rate — even accounting for MPP — may indicate deliverability problems. If your emails are landing in spam folders rather than inboxes, opens will plummet. Monitoring open rate trends over time remains useful for spotting deliverability deterioration before it becomes critical. A gradual decline can signal list fatigue or sender reputation issues worth investigating.

3. Benchmark Campaign Performance

Despite MPP’s distortion, open rates are still widely reported and benchmarked across the industry. For internal performance tracking — comparing your campaigns against your own historical data — they provide continuity. Many email marketing platforms also offer Apple MPP-adjusted open rate estimates that attempt to separate proxy opens from genuine ones, providing a more accurate signal.

Examples

1. Subject Line A/B Test

An e-commerce brand tests two subject lines for the same promotional email: “New arrivals this week” vs. “Your size is back in stock — but not for long.” The second subject line produces a 35% open rate vs. 22% for the first. Even accounting for Apple MPP inflation affecting both equally, the relative difference is meaningful — the urgency and personalization of the second line genuinely drives more opens.

2. Interpreting a Post-MPP Spike

A nonprofit’s monthly newsletter suddenly shows 52% open rates after years averaging 28–32%. The development team celebrates — until they investigate and discover that Apple Mail users comprise 45% of their list and MPP became widely adopted during this period. The absolute number is inflated by proxy opens, but the adjusted rate (approximated by removing likely MPP opens) is closer to 30–33% — consistent with historical performance.

3. Shifting Focus to Click-Through Rate

A SaaS company tracks both open rate and click-through rate for their monthly newsletter. Post-MPP, they observe their open rate is no longer reliably comparable month-to-month. They shift their primary KPI to unique CTR, which is unaffected by MPP (Apple’s servers don’t click links). Their CTR data shows consistent, meaningful variation between campaigns — a more reliable basis for optimization decisions.

Common Mistakes to Avoid

  • Treating post-MPP open rates as ground truth — A 45% open rate that’s mostly Apple proxy opens doesn’t mean your content is resonating. Celebrating inflated numbers can mask real engagement problems. Always contextualize open rates with click data and conversion data.
  • Ignoring open rates entirely — The opposite mistake. Open rate still provides relative and trend data that’s useful when interpreted correctly. Writing it off entirely abandons a useful signal.
  • Not segmenting by email client — Many ESPs (email service providers) show which email clients your subscribers use. Segmenting by Apple Mail vs. non-Apple-Mail subscribers gives you a more accurate picture of actual open rates from the portion of your list that isn’t affected by MPP.
  • Using open rate alone to evaluate list hygiene — Before MPP, low open rates identified disengaged subscribers worth pruning. Post-MPP, some non-openers may actually be reading (Apple Mail shows them as opened automatically) while some “openers” may not be real. Supplement open rate with click data and last-purchase/conversion data for list hygiene decisions.

Best Practices

1. Prioritize Clicks and Conversions as Primary Metrics

Click-through rate and conversion rate are more reliable measures of email engagement in the post-MPP era. A subscriber who clicks a link has definitively engaged; the data is unambiguous. Build your email optimization strategy around maximizing clicks to relevant content, purchases, or other conversion goals — not around maximizing the open count.

2. Use MPP-Adjusted Reporting When Available

Major ESPs (Klaviyo, Mailchimp, ActiveCampaign) have introduced Apple MPP filtering in their reporting. This identifies Apple Mail opens that are likely proxy-generated and separates them from probable human opens. Using this adjusted data provides a more accurate baseline for trend analysis and benchmarking. The methodology isn’t perfect, but it’s substantially more useful than raw open rates.

3. Monitor Trends, Not Just Absolute Numbers

A consistent 28% open rate that suddenly drops to 18% over two months is a meaningful signal, regardless of whether the 28% baseline was inflated by MPP. Trend monitoring identifies deliverability problems, list fatigue, and content effectiveness shifts that absolute benchmarks can’t. Compare your own campaigns to your own history first; use industry benchmarks as a secondary reference point.

Frequently Asked Questions

What is a good email open rate in 2024?

Industry averages vary widely by sector, with typical ranges of 20–45% depending on whether MPP inflation is accounted for. Rather than comparing to benchmarks, compare your current campaigns to your own historical baseline — that’s the most relevant reference point. A consistent trend is more informative than any single number.

Has Apple MPP made open rates useless?

Not entirely — they’re less reliable as an absolute measure of engagement, but they retain value for trend analysis and relative comparisons (A/B tests where both variants are equally affected by MPP). Clicks and conversions are now the primary engagement metrics, with open rates serving as a supplementary signal rather than the headline number.

How do I improve email open rates?

Subject line quality is the primary lever — specific, benefit-driven, or curiosity-driven subject lines outperform generic ones. Sending cadence matters too: emailing too frequently trains subscribers to ignore you; too infrequently reduces familiarity. List hygiene (removing disengaged subscribers) also lifts rates by concentrating sends on your most engaged segment. Preview text (the snippet visible in email clients beside the subject) is frequently overlooked and worth optimizing.

Should I send emails specifically timed to maximize open rates?

Timing optimization is real but often overstated as an impact driver. Testing different send times can produce 2–5% open rate improvements, but subject line quality and content relevance typically have larger effects. Most ESPs offer send-time optimization tools that learn from your specific list’s behavior — using those tools is reasonable once higher-priority optimizations are in place.

Related Glossary Terms

How CyberOptik Can Help

Email remains one of the highest-ROI channels in digital marketing, and understanding metrics like open rate — including what they can and can’t tell you in the current landscape — is key to making it work. Our team can help you build campaigns that reach the right people and drive real engagement. Contact us to discuss your email strategy or learn about our marketing services.