Outlook 2013 winmail.dat attached to email when sending with email signature
Do you get a winmail.dat file attached when you send your email signature in Outlook 2013. Here's the fix:
Open Outlook 2013
You need to change the message format for all messages to be sent in "HTML" not as "Rich Text" or "Plain Text".
Click the File tab.
Under Compose messages, in the Compose messages in this format list, click HTML.