The way most messages are measured is through the use of a 1 pixel by 1 pixel transparent image, usually called an image beacon. This image can be measured so that the sender can determine if a message has been opened or not. However, Apple introduced a new feature called Mail Privacy Protection (MPP) with the rollout of iOS 15.
Proxy devices are email platforms that are trying to protect their users by making requests on their behalf. Google, Yahoo, and others also use proxies; however, those services disclose that the User Agent is a proxy, whereas Apple does not.
Apple uses an "Apple Email Image proxy" that acts as the User Agent and downloads all the images on behalf of the recipient. This registers the message as having been opened (and engaged) even though the recipient may actually not have done so, which results in inflated metrics. This will occur with any recipient using the Apple Mail app on a device using iOS 15 or later. However, PoliteMail prevents this from happening! PoliteMail has developed proprietary technology that, by turning on iOS Measurement, a message can still be effectively measured even with MPP in place.
How PoliteMail Handles Proxy Devices
Since proxy opens are performed by the service (probably on what PoliteMail will register as a desktop device) and not the user, PoliteMail has introduced the Proxy devices metric to indicate when a proxy device open is detected. This keeps the metrics accurate for all devices.
So, are Proxy Opens Included in the Open Rate?
It depends! User-present proxies, where a proxy may be used to open the message but the user is present and part of the process, will count towards the open rate. However, when the user is not present, such as an Apple proxy without the user, are not.