How to show and hide something in Outlook
Proper mso code for Outlook version 9+
by Wally Glenn
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta name="viewport" content="width=device-width">
<title>Outlook Images</title>
</head>
<body style="background: #ffffff !important;">
<table>
<tr>
<td>
<!--[if !mso]><!-- -->
<img src="http://via.placeholder.com/300x300/0000ff/?text=Modern+Email" alt="Modern+Email" width="100%" style="display:inline-block;border:none;outline:none;padding:0;margin:0;width:100%;height:auto;" border="0" hspace="0" vspace="0">
<!--<![endif]-->
<!--[if gte mso 9]>
<img src="http://via.placeholder.com/300x300/ff0000?text=Outlook" alt="" width="100%" style="display:inline-block;border:none;outline:none;padding:0;margin:0;width:100%;height:auto;" border="0" hspace="0" vspace="0">
<![endif]-->
</td>
</tr>
</table>
</body>
</html>