The default deocument mode of WLM is ie7. It causes this problem.
The registry file makes it to be ie11.
ie11.eml
MIME-Version: 1.0
Content-Type: multipart/alternative;
boundary="----=_NextPart_000_052F_01CF79BB.B0ED4A20"
X-Priority: 3
X-MSMail-Priority: Normal
Importance: Normal
X-MimeOLE: Produced By Microsoft MimeOLE V15.4.3555.308
X-Unsent: 3
This is a multi-part message in MIME format.
------=_NextPart_000_052F_01CF79BB.B0ED4A20
Content-Type: text/plain;
charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
------=_NextPart_000_052F_01CF79BB.B0ED4A20
Content-Type: text/html;
charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
<HTML><HEAD>
<meta http-equiv="X-UA-Compatible" content="IE=11" >
</HEAD><BODY>
<a href="http://www.microsoft.com">aaa</a>
</BODY></HTML>
------=_NextPart_000_052F_01CF79BB.B0ED4A20--
ie7.eml
MIME-Version: 1.0
Content-Type: multipart/alternative;
boundary="----=_NextPart_000_052F_01CF79BB.B0ED4A20"
X-Priority: 3
X-MSMail-Priority: Normal
Importance: Normal
X-MimeOLE: Produced By Microsoft MimeOLE V15.4.3555.308
X-Unsent: 3
This is a multi-part message in MIME format.
------=_NextPart_000_052F_01CF79BB.B0ED4A20
Content-Type: text/plain;
charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
------=_NextPart_000_052F_01CF79BB.B0ED4A20
Content-Type: text/html;
charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
<HTML><HEAD>
<meta http-equiv="X-UA-Compatible" content="IE=7" >
</HEAD><BODY>
<a href="http://www.microsoft.com">aaa</a>
</BODY></HTML>
------=_NextPart_000_052F_01CF79BB.B0ED4A20--