That’s really nice analysis. Mailchimp is the biggest one as I guessed. Don’t know if you count the spam folder since some marketing emails could be automatically sent there.
Sendgrid: 30.2%
SES: 16.8%
Mailchimp: 16.8%
"Amazon SES only supports open tracking over HTTP domains."
https://docs.aws.amazon.com/ses/latest/DeveloperGuide/config...
Yes, big webmail providers fetch the tracking pixels for you and serve them to your browser over HTTPS, but not every mail provider does that, sometimes for good reason, leading to problems like this:
https://protonmail.com/support/knowledge-base/connection-not...