AutomateWoo

Sending a plain text version with the HTML version in a multi-part format can improve email spam scores.
We could automatically generate the plain text version based of the supplied HTML.
Ref: https://www.campaignmonitor.com/blog/email-marketing/2019/03/html-vs-plain-text-emails-everything-you-need-to-know/
Note: WP can’t currently handle multi-part emails but a fix has been proposed: https://core.trac.wordpress.org/ticket/15448