Image style height and width not taken in outlook mails

Put the width and height in separate attributes, with no unit:

<img style="margin: 0; border: 0; padding: 0; display: block;"
src="https://stackoverflow.com/questions/20989897/images/img.jpg" width="120" height="150">

Another Option:

<!--[if gte mso 9]>
<style type="text/css">
img.header { width: 600px; } /* or something like that */
</style>
<![endif]-->