SmartTemplate4

If you write html templates for your e-Mail you should first have to know that you don't write complete html files like for websites.
Please don't write something like this in your e-Mail template:

   <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
    "http://www.w3.org/TR/html4/loose.dtd">
   <html>
     <head>
      <meta http-equiv="content-type" content="text/html; charset=UTF-8">
      <title> </title>
     </head>
    <body>
    </body>
   </html>

If you write this you cause some trouble because this will paste automatically from your mailclient by default.
Your e-Mail content itself will be embedded only.

   <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
    "http://www.w3.org/TR/html4/loose.dtd">
    <html>
     <head>
      <meta http-equiv="content-type" content="text/html; charset=UTF-8">
      <title> </title>
     </head>
    <body>
     <div>your content inside div tag</div>
     <span>your content inside span tag</span>
    </body>
   </html>

inline style or the style tag

Now this is a question of flavour which variant you use, choose what you prefer.
Some user swear by inline style and other swear by the style tag.

The <style> tag

A nice of way of styling is using css classes. A css class is a name of your choice, starting with a full stop (.) It can be used in any html tag by adding the html attribute class="name of the class".
Advantage: it can be used on multiple elements to make them look the same without lots of copying and pasting of style attributes.

   <style type="text/css">
   .myLine {
     font-family: "Comic Sans MS",cursive;
     font-size: 30pt;
   }
   </style>
   ...
   ...
   <div class="myLine">my line</div>

Styling "inline"

This is the most robust way of styling because it will always "stay" with the element (here: div) no matter where you move it or whether it is quoted in another email.
Disadvantage: If you want to style 2 elements the same way you have to copy/paste the whole lot.

   <div style="font-family: 'Comic Sans MS',cursive; font-size: 30pt;">my line</div>

The visual result is for both variants the same
Style tag results

TIP: The only difference between both variants is the way you write font names with white-space
style tag = "inside double quote marks"
inline = 'inside single quote marks'.