I know that you can track whether a user has viewed an email with a 1px image; are there other ways too? Since a lot of email clients have been blocking externa

I know that you can track whether a user has viewed an email with a 1px image; are there other ways too? Since a lot of email clients have been blocking external images for a long time, I figure either the quality of the metric must be pretty bad these days or a better method has emerged. Preferably the latter so I can learn something new :)