Understanding Email Open Rates in the Age of Apple MPP

What Is Apple Mail Privacy Protection (MPP)?#

In September 2021, Apple launched Mail Privacy Protection (MPP) as part of iOS 15, macOS Monterey, and iPadOS 15. When enabled — and most Apple Mail users have it enabled — MPP:

1. Pre-fetches all images in emails, including the invisible 1×1 tracking pixel that records opens
2. Routes this pre-fetching through Apple's proxy servers, masking the user's real IP address and location
3. Does this regardless of whether the user actually opens the email

The result: every email delivered to an Apple Mail user with MPP enabled registers as "opened" — even if it sits unread in their inbox forever.

How Widespread Is MPP?#

Apple Mail is one of the most popular email clients globally:

• iOS Mail accounts for roughly 35–50% of all email opens (varies by list/industry)
• Of those, 80–90% of iOS 15+ users have MPP enabled
• This means 30–45% of your "opens" may be MPP-inflated, depending on your audience

The higher the proportion of Apple Mail users on your list, the less meaningful your raw open rate is.

Identifying MPP Inflation in AcelleMail#

AcelleMail's campaign reports include client/device data where available. Look for:

1. Go to your campaign report → Open Statistics → By Email Client
2. Note the percentage of opens attributed to Apple Mail / iOS Mail
3. If Apple Mail opens suddenly spiked after September 2021 (compared to your historical average), that delta is your MPP inflation

Calculating a corrected open rate:

Raw open rate:                 55%
Apple Mail opens % of list:    40%
Actual Apple users who opened: Unknown — MPP pre-fetched for all 40%

Conservative estimate:
  Non-Apple opens:             15% (these are real)
  Apply historical Apple open% (from pre-MPP data): 25% of the 40% = 10%
  Estimated real open rate:    ~25%

This is imprecise, but it gives context. The key is recognizing that a post-2021 open rate of 55% does not mean what a 55% open rate meant in 2019.

What to Measure Instead#

Since open rates are unreliable for MPP-affected audiences, shift focus to these metrics:

1. Click-to-Open Rate (CTOR)#

CTOR = (Unique Clicks / Unique Opens) × 100

This ratio tells you how compelling your email content is to those who opened it. It's less affected by MPP because clicks require real human action.

2. Click Rate#

Click Rate = (Unique Clicks / Emails Delivered) × 100

Clicks are not pre-fetched by MPP. A click requires the subscriber to actually open the email and interact with a link. This is the most reliable engagement metric in the post-MPP world.

3. Conversion Rate#

Track downstream actions: purchases, signups, downloads. Use UTM parameters to attribute these to specific campaigns in Google Analytics.

4. Revenue per Email#

Revenue per Email = Total Campaign Revenue / Emails Delivered

For e-commerce, this is the ultimate metric — it directly measures campaign profitability regardless of open tracking.

5. Unsubscribe Rate#

A real behavioral signal — subscribers actively choosing to leave. Monitor this carefully as a proxy for content relevance and frequency.

Adjusting Automation Triggers#

If you use open events to trigger automations (e.g., "subscriber opened email → enter follow-up sequence"), MPP will trigger these for all Apple Mail users, including those who never saw your email.

Fix: Replace open-based triggers with click-based triggers wherever possible.

In AcelleMail's automation builder:

• Instead of: Trigger: Subscriber opened Email X
• Use: Trigger: Subscriber clicked link in Email X
• Or: Trigger: Subscriber did NOT click any link in Email X (within 5 days) → send follow-up

Segmentation Impact#

List segments built on "opened in the last 90 days" now include MPP false positives. Review any segments that use open behavior as a primary condition and add a click condition as a secondary qualifier:

Segment "Engaged Subscribers":
  BEFORE MPP: Last opened ≥ 1 email in 90 days
  AFTER MPP:  Last clicked ≥ 1 link in 90 days
               OR Last opened ≥ 1 email in 90 days
               AND Email client NOT Apple Mail

The Bottom Line#

Open rates are not dead — they're just less precise. Use them as a directional trend (did this campaign perform better or worse than your average?) rather than an absolute measure of engagement. Build your primary reporting around click rates, conversion rates, and revenue — metrics that Apple's proxy servers cannot inflate.