LH Multipart Email gives every HTML email your WordPress site sends a plain text version alongside the HTML, so each message goes out as a proper multipart email.
WordPress, BuddyPress and most plugins send HTML-only email. A message with no plain text part is more likely to be marked as spam, and readers whose mail client shows text, or who use a screen reader or a watch, can end up with raw markup or nothing at all. This plugin fills the gap automatically, with nothing to configure.
wp_mail(), from core, BuddyPress or any plugin.WordPress 5.5 or later and PHP 7.3 or later, with the PHP DOM extension. The html2text library is a Composer dependency, so after installing from GitHub run composer install --no-dev in the plugin folder. Until it is installed, emails are sent HTML-only.