If you received an attachment that you want to delete, you can easily delete it, freeing up valuable disk space.
First, open the email that contains the attachment. You should see it at the bottom of the email.
Right click the attachment icon and click ‘Show in Finder’.
You should then see the attachment in Finder. Simply select the attachment and then move it to trash to delete the email. Note: The file will be in Trash, you will need to empty trash to completely remove it from your Mac.