I'm trying to slim down my email archive by removing attachments I no longer need, using the "Message > Remove Attachments" command in Apple Mail.
After removing several GB worth of attachments within Mail, I noticed that my ~/Library/Mail/ folder wasn't getting any smaller. Digging into the folder structure, I found that all of the attachments I had 'removed' from the emails are still present in the filesystem, deeply nested in the ~/Library/Mail/ folder.
I've tried quitting and restarting Mail, rebuilding the mailboxes, and restarting the computer, but the files remain.
Are others experiencing this behaviour? Is it possible to have the attachments removed from the hard drive when 'removed' from the email?
Running macOS Sierra 10.12.6