Having troble in 1.7 while set Content-Type to text/html

Postman worked really fine in 1.6 version, and while I just updated to 1.7 yesterday, all emails sent in text/plain except the test email.
My site is using a theme to handle email content, and that them can’t determine the content-type so I used to use Postman to handle the smtp settings and force to reset the content-type to text/html. But this setting doesn’t work in 1.7 version
Please help me 🙁

https://wordpress.org/plugins/postman-smtp/