Hi Stefan,
You have 3 mistakes in your code.
1) You call the method for string "MacroMethod", but you need to call this method for object which data you want to show, e.g. CurrentUser.ApplyTransformation. And you can show all properties of the object in the transformation
2) You can apply transformations of the Text/XML and HTML type via macro expressions. It means that you can use K# syntax to show object properties in the transformation, e.g. for example above to show user first name: {% FirstName %}. But you wrote {% #Eval() %} this is wrong construction, because you mixed K# syntax and ASPX syntax.
Please, see this link https://docs.kentico.com/display/K81/Using+transformations+in+macro+expressions
3) If you add some custom fields to MacroResolver, you can show this fields without transformation in email template.
For your code it will be:
<div>{% Name %}</div>
<div>{% Email %}</div>
<div>{% Telephone %}</div>
https://docs.kentico.com/display/K8/Adding+custom+macro+fields