It seems the only way to track “open rates” is to include an image in the email in which the recipient has to download using their email client. We wanted to send out plain text emails only.
What's the best way to track open rates and in particular for plain text emails?
Mailwizz also tracks opens when links inside the email are opened and tracking links is enabled, so you can hope that a url from your plain email is opened, thus open tracked.
Otherwise there's no other way.