All you need is a HTML container with an editable region called ‘main’:
<div mc:edit="main"></div>
This thread might help you understand Mandrill templates and Merge Vars and how to use them in wpMandrill:
http://wordpress.org/support/topic/understanding-wpmandrillmail?replies=6#post-4244274
Also, this KB article has interesting information on editable regions:
http://help.mandrill.com/entries/21694286-How-do-I-add-dynamic-content-using-editable-regions-in-my-template-
Do I need the “div tags” or can I just have mc:edit=”main” anywhere?
I don’t know how to add content to a template, for user registration email. Can you please tell me what tag to add?
I try <div mc:edit=”main”></div> but no result.
If a don’t select any template, the email is sent ok, with the right text content.
But if I select a template, no custom text is added to the message.