I just set mine up.
I set an association from the main object I was working on to the Email module.
I then did the same for attachment.
Then I added the server setup pages to my app, logged in and set my server info.
Once I did that, I created a new Email object on the page I was working on,
inside of this view I took some of the email templates they had included (under admin > email I believe) and set the FROM, TO, HTML etc… Fields.
On save on my actual item I was working on I called a microflow and inside of this I set the emailassociation to my other object.. Any email info you have at this time (in a microflow) can then be added to the email object.
Once that is done, you can add the ivk_send_email (something like that) microflow included with the email application in your current save flow. This is what worked for me, but I’m not going to lie, it took a bunch of time.
I use the Email with Templates module. It provides complete functionality for sending emails from your Mendix app. You can read about how to configure it here: https://docs.mendix.com/appstore/modules/email-with-templates