How to find out if EngageOne Digital Delivery supports .ehtml file type

Product Feature: Operational Settings
eMessaging (EODD_2.1.1_Build_551_17096 and previous) supports only .html files for email body document.

If we use .ehtml for email body, we will end up with the following error in e-messaging when sending the email through e-messaging:
"Error in processing, html file missing or invalid html file".
UPDATED:  November 3, 2017