I recently found that the horizontal lines <hr> tags are not rendering in MS Outlook 2016 on windows only (renders in all the other stubborn MS Outlooks 2000/2003/2010 etc.,). It even renders it properly in MS Outlook 2016 for Mac.

This is the simple test case I used in Litmus

<hr style="background: #d9d9d9; border: none; color: #d9d9d9; height: 1px;" />
<hr style="background: #d9d9d9; border: none; color: #d9d9d9; height: 1px;" />
<hr style="background: #d9d9d9; border: none; color: #d9d9d9; height: 1px;" />
<hr style="background: #d9d9d9; border: none; color: #d9d9d9; height: 1px;" />

Ideally four horizontal lines should appear, but none appear on Outlook 2016 on windows. Any help is appreciated.

Outlook 2016 for Mac
Outlook 2016 for Windows