Removing [Old] Mail Attachments from El Capitan's Mail Application

[theALmighty66]

As I just posted here <Removing Attachments> :

I'm really thinking about removing all mail attachments myself to free a LOT of hard disk space—but I'm not sure the best way to go about it.

Using El Capitan, what's the best & most efficient way to remove attachments, namely old email attachments from both the Inbox & Sent box?

Already I made a smart folder with all messages from over a month ago with attachments—and tried to select them all & drop down Message to Remove Attachments — but that doesn't do anything. All the messages linger in that smart folder...with attachments still there.

Any advice?

Thanks, y'all!

 

[honestone]

Do you need the "base" EMails which contains the attachments?

 

[theALmighty66]

I don't need them, but I'd prefer to keep them if possible.