Mixmax has an accidentally helpful guide to the only way to block tracking: block images. (They also mention how aggressively they try to get around email blockers.)
There's an inverse relationship between email importance and production value, seeing a bunch of blank boxes is a great hack to signal that.
The recipient opens the email on a legacy email client that blocks all images from being viewed. This also means that images in signatures and other media won't carry through to the recipient, so in practice this is quite rare.
The recipient has software to block email tracking. This is also quite rare, and Mixmax actually circumvents most email tracking blockers."
There's an inverse relationship between email importance and production value, seeing a bunch of blank boxes is a great hack to signal that.
https://success.mixmax.com/article/57-track-opens
"...An open won't be recorded if:
The recipient opens the email on a legacy email client that blocks all images from being viewed. This also means that images in signatures and other media won't carry through to the recipient, so in practice this is quite rare.
The recipient has software to block email tracking. This is also quite rare, and Mixmax actually circumvents most email tracking blockers."