You haven’t listed seven steps to open an email attachment. When I get a pdf attachment I either save it to the desktop and open it later or I click on the pdf icon in the text box and Acrobat Reader opens it. Same with a jpeg or gif, except they frequently appear in the text box when the email is opened, no clicking required (only if I want to save to the desktop). Don’t know what WMP is, and nothing is downloaded to preview. You do appear to have the only Mac that doesn’t work right.
WMP is Windows Media Player which is needed to open attachment of WMV Windows Media Video.