Joe and Jill are fairly efficient in keeping their scopes narrow on usability. So, if signing were properly featured, then the failing emails would get burried

Joe and Jill are fairly efficient in keeping their scopes narrow on usability. So, if signing were properly featured, then the failing emails would get burried in Spam folder, even more, the email client could block the 'Click here so I could screw you' links in such emails, and more choices how to integrate it in common user's flow. However, the other question is rather if the email signing would still serve the purpose in case when the system/server gets compromized, keys stolen. Did any major company paid off fully what's due for losing away scores of users' private details? The errosion of trust may be more detrimental to Joes and Jills outhere.