The short answer: manufacturers should measure email by what it does for the pipeline, not by open rates. Replies, conversions and lead-to-opportunity rate show whether email is moving buyers forward. Since Apple Mail Privacy Protection, opens are too inflated to guide decisions on their own.
Email is still one of the most effective ways to stay in front of engineers, buyers and plant leaders through long industrial sales cycles. The way to judge it has changed, though, and many manufacturers are still reading the wrong numbers.
In September 2021, Apple introduced Mail Privacy Protection (MPP) for its Mail app. With MPP turned on, Apple loads email content, including the tracking pixel that records opens, in the background. That means a message can register as opened even if no one looks at it.
Because Apple Mail is widely used, MPP inflated open rates across the industry. Corporate security filters that scan links and images add more false opens and even false clicks. The result: an open rate can look healthy while real engagement is flat, and subject line tests based on opens can point you in the wrong direction.
| Metric | What it measures | Why it matters |
|---|---|---|
| Reply rate | Recipients who respond to the email | The clearest sign of real interest, especially for sales-led emails |
| Conversion rate | Recipients who complete the action you asked for, such as a quote request or download | Ties the email to a business outcome |
| Click-to-open rate (CTOR) | Unique clicks divided by unique opens | Useful for comparing content between campaigns |
| Lead-to-opportunity rate | Email-sourced leads that become sales opportunities | Shows whether email moves buyers into the pipeline |
| List growth rate | New subscribers minus unsubscribes and bounces | Shows whether your audience is growing or shrinking |
| Unsubscribe and spam complaint rates | Recipients who opt out or report the message | Early warning for relevance and deliverability problems |
Open-based subject line tests are no longer reliable. Instead, test the things that drive action and measure the result by clicks, replies or conversions:
Email is the connective tissue of an industrial marketing program. It nurtures leads that SEO and AI search and paid search bring in, keeps current customers engaged for cross-sell and upsell, and sets up timely teleservices follow-up when a contact shows buying signals. Learn more about our approach to email marketing for manufacturers.
Not reliably. Since Apple Mail Privacy Protection launched in 2021, Apple Mail can load email content automatically, which registers as an open whether or not someone read the message. Other privacy tools and security filters cause similar distortions.
Click-to-open rate (CTOR) is unique clicks divided by unique opens. It shows how compelling your content was to people who opened it, though it inherits some distortion from inflated opens, so use it to compare campaigns rather than as an absolute measure.
The most useful metrics tie email to pipeline: reply rate, conversion rate on the action you asked for, and lead-to-opportunity rate. Track list growth and unsubscribe and spam complaint rates to keep your list healthy.
Most industrial audiences respond well to a steady monthly newsletter plus targeted sequences triggered by behavior, such as a spec sheet download or a quote request. Consistency and relevance matter more than volume.
In the U.S., CAN-SPAM allows commercial email to business contacts without prior consent, but requires accurate sender information, a clear subject line, a physical address and a working unsubscribe link honored within 10 business days. Canada and the EU have stricter consent rules.
If you want a clear picture of where you stand, schedule a 30-minute strategy call. You will walk away with at least three actionable ideas, even if we never work together. You can also see what we have done for other manufacturers in our success stories and client testimonials.
