Mail won't "let go" of attachments I send
When I drag a file from the desktop to an email and send it, I then drag the file from the desktop to the trash but whenever I come to empty the trash (even if it's several days later) I get the error message that that file is in use by another application. I can empty the trash by either quitting Mail or using the Delete Immediately option but surely Mail shouldn't still be using the file?
OS X El Capitan (10.11.6), Mac Pro Quad Core