For this you have to download the
Mx reflection module ,:
email module with template and
Encryption module from marketplace.
After that copy the administrator snnipet from emailtemplate and mxObject from reflection module and paste in your module .and add one blank page and drag tab and drop it in page and after that drag this copy item drop in this tab .And copy submicroflow from emailtemplate(SubSendSimpleEmail).And paste in your module and add one parameter in your microflow as string type. and set htmlbody as that new parameter.
also follow the this link:https://docs.mendix.com/appstore/modules/email-with-templates
Plz let me know if you have a get an errors.
There are several HOW-TO’s available, for example this one. Might this how-to is helpfull.