An email report shows opens and clicks within minutes of a send. It is tempting to treat them as a scoreboard. Both numbers measure something narrower than they appear to, and neither tells you what happened on the website. This article explains what each metric records, where it breaks, and how to connect a campaign to outcomes in GA4.
How opens are recorded, and why they drift
An open is not a person reading. It is an image request. Mailchimp's help page on open and click rates describes a tiny, transparent image loaded into each email. When the image loads, the open is counted. If the recipient's client blocks images, the open is not recorded. Mailchimp counts a click as an open even when the image never loaded.
Apple's Mail Privacy Protection (MPP) breaks this in the other direction. Apple's iPhone User Guide says the feature hides the recipient's IP address and "prevents senders from seeing if you've opened the email message." Apple's privacy notice for the feature adds that Mail downloads remote content in the background by default, even if the email is never opened, through two relays.
The result, as Mailchimp's MPP FAQ puts it, is that emails in Apple Mail are reported as opened regardless of what the contact did. The same FAQ notes that MPP limits location estimates.
So the open count mixes two errors. Image blocking hides real reads. MPP adds opens that never happened. Because the share of each depends on your list, open rate can move when the audience's mail apps change, with no change in interest.
