cfmailparam disposition filename does not work in outlook

I have a very simple example for sending an image as an attachment using Coldfusion 11 cfmail tag.

<cfmail to="example@domain.com" from="example@domain.com" subject="Test" type="html">

     <cfmailparam

          file="www.example.com/image.png"

          disposition="attachment; filename=""test.png""">

</cfmail>

I want the attachment to be called "test.png" when it is viewed in the recipients email client.

It works fine when I receive the email in Gmail, however Outlook 2013 (and Office 365 web client) retains the "image.png" attachment name.

Have I correctly made use of the "disposition" attribute?