In my Outlook 2013, I attached a .msg format attachment to an email. Its display name is the subject of the msg file instead of the file name of the msg and also it is not showing any extension like xyz.msg. I tried different email format (HTML, rich text and plain text) and the result is the same. For other files, attachments are also displayed as their file name and extension like .xlsx,.txt,.., just msg having this issue. Any idea why Outlook is having this behavior?