How to Remove Attachments in the Mail app in 10.12 Sierra The Mail app in earlier versions of OS X had a usable Remove Attachments menu item in the Message menu in OS X's built-in Main app.  It allowed me to remove large photos (etc.), and shrink down the valuable SSD storage used by the Mail app.

But in macOS Sierra, the Remove Attachments menu item is sometimes grayed out.  

So how do I remove attachment in received email, where I want to keep the text of the email, but not the (large photos, etc.) attachments?

Is there some Mail app setting needed?  Or do I need to do some Terminal command-line kung-fu to get rid of all those unwanted attachments taking up space on my SSD?

Added: The email is being downloaded from a POP email account, if that makes any difference.

Added: New info.  Some email messages shows a paperclip in both message browser and in the opened email window.  Those allow Remove Attachments.  However some email messages only show a paperclip in the center hover toolbar in the opened email viewer, not in the message browser.  Those ones have Remove Attachments greyed-out.  Is there a way to remove attachments (as shown by the paperclip toolbar) from those emails messages?  Why is there a difference between the two types of attachments?
The Messages > Remove Attachments selection is greyed-out unless you have selected (in the Mail message viewer) one or more emails which contain attachments. Select one or more emails which contain attachments and the selection will be available.