I have deleted the Windows 8 mail app for exactly that reason, drove me nuts and it seems there is no fix. I simply access gmail through the link on Chrome.
well! I am baffled to say the least.. I have lots of emails with attachments (photos) that date back yrs...I have try to delete them and thought I had cracked it! but! although I have deleted the emails and attachments the blighters are back next time I look!! it says that if I delete the photos with the attached email that they will be in the trash bin, but!! they never seem to get there...any ideas anyone?