1. How to fix linked images blue border in Windows Mail?
Some email clients and webmail services, including AOL Mail, Gmail, Lotus, Outlook, Thunderbird, and Windows Mail, will display a blue or black border around linked images that do not have a border specified.
You can easily set the img border element to 0 using HTML or CSS, or you can set the border to 0 using CSS.
HTML Solution
<a href='http://www.maool.com' title="mailmouse"target="_blank">
<img src="test.jpg" width="500 "height="300 "border="0 ">
</a>
CSS Solution
<a href='http://www.maool.com' title="mailmouse"target="_blank">
<img src="test.jpg" width="500 "height="300 "border="0 " style="display:block; border:0; 20px;">
</a>
The display:block; style was added to Gmail and Yahoo! Mail to prevent image gaps.
Alternatively, to be safe, you can combine both solutions.
HTML + CSS Solution
<a href='http://www.maool.com' title="mailmouse"target="_blank">
<img src="test.jpg" width="500 "height="300 "border="0 " style="display:block; border:0; 20px;">
</a>
2. How to target Windows 10 Mail App using Conditional Comments?
Conditional comments can be used to target the Windows 10 Mail App in the same way that they can target the Outlook email client.
<!--[if mso 16]>
{Place your content here}
<![endif]-->
As version 16 is greater than 9, the standard!–[if (gte mso 9)|(IE)]> declaration will also work.