[rossdavidh]

The data I've seen suggests the opposite?

[legitster]

All of our internal tests have confirmed this, and even the email providers have more or less confirmed the same thing: https://blog.hubspot.com/marketing/plain-text-vs-html-emails...

[eastern]

That's HTML emails _pretending_ to be plain text.

Meaning the 'plain' text is Html-formatted to look plain and there are tracker links and probably tracking pixels too.

Real plain text should be just like something a human being typed.

Also, ignoring the general scamminess of hubspot, the linked article says html mail is MORE likely to be flagged as commercial. The article, in fact, is entirely pro plain text.