When comparing sender engagement data with Yahoo's VTO engagement data, senders should expect similar but not necessarily the exact same results.
For additional information on pixel tracking data, please read:
Pixel tracking data
Pixel tracking data counts an "open" when an image is retrieved from a server. However, some email applications retrieve images prior to delivering an email to a subscriber. This activity counts as an "open" even if the subscriber does not open the email.
Opens are also not counted when an email application caches images on their own proxy server or when a subscriber opens an email with images suppressed.
The result of this third party interaction and subscriber behavior related to pixel tracking leads to inflated and incorrect open rates.
Yahoo's VTO engagement data is based on actual subscriber interactions within their mailbox and does not use pixel tracking.