I use that "Edit HTML" button on the regular, to make HTML adjustments in a variety of different types of emails I send. This is a screenshot from the toolbar in Zoho Mail's email editor. I noticed recently it is just not available - can't click it, can't open up the HTML version of the email.

I found this odd, and thought maybe it was just an email to a particular recipient (ie. the recipient requests text-only emails). But upon drafting a new message, the button was still unavailable.

I sincerely hope this is just a glitch, or maybe I inadvertently disabled it somehow. Removing this functionality would put a massive dent in my Zoho Mail user experience.