I meant if I'm sending both HTML and text versions to everyone, what's the number of people who are only getting the text version due to their server settings.
I know you can't track opens, but back in the day with early email marketing tools you could see how many were getting the HTML version blocked, but I know much has changed.
It sounds like the 'delivered' quantity isn't trackable by Marketo, but I did find a thread where Marketo will put in a trackable link if you put double brackets around the link in the text email: [[www.example.com]].
If anyone knows how to track delivered text-only emails, would love to hear it.