How does gmail open tracking affect the gross opens rate

Google handles email tracking images that are sent to gmail addresses differently than other email providers. This difference affects how gross opens are tracked.

The first time a contact opens an Acoustic Campaign email and downloads images, Gmail responds to the 1x1 tracking pixel and triggers the initial open. But, subsequent opens cause gmail to load the tracking pixel from its own cache. Unique open rates are not affected since the initial open still triggers that contact's unique open pixel. Because gmail references the tracking pixel from gnail servers, there is no way for Acoustic Campaign to see whether the pixel was reloaded on the contact's side. So, gross opens from gmail are not a reliable way to measure multiple opens.