Sending emails in plain text improves deliverability because they are less likely to trigger spam filters, are universally supported across all email clients, and are perceived as more authentic.
Their simplicity reduces technical issues and processing time, while avoiding complex elements that can be associated with phishing, making them more likely to reach the recipient's inbox.
If you're looking to improve your deliverability by sending emails in plain text, without HTML, head to your campaign settings, and enable 'Optimise Email Delivery'
Clicking on DON'T track email opens and link clicks also allows you to send emails in plain text. (As long as Optimise Email Delivery is disabled as well)
**Note 1: You can only enable/disable this feature when a campaign is drafted. Once you start your campaign, you can no longer change this setting.
** Note 2: When optimizing email delivery, Open Rate and Click Tracking will be disabled, and unsubscribe links, along with other HTML links, will be removed from the email.