There's a big difference between "self-destructing gmail" and "self-destructing email".
Even with the first, Google supports forwarding all mail to an arbitrary email address, which means the "Gmail" becomes a text-file stored on a dovecot server (or other regular mail server) somewhere.
So unless they break delivery (you can forward only some subset of emails) - there's no way for the sender to have any better guarantee than "please delete after reading".
At least the pgp spec has (had?) an "eyes only" flag that, while it didn't guarantee anything, at least meant compliant software would try hard to not leave a plain text copy on the filesystem.
just store the contents locally, and replace the body with some URL that the user has to click..
then, when non-gmail users have been desensitized to clicking links in emails 'because gmail', and get viruses constantly, sell them gmail as a way to have email without risk of viruses.
Not sending the content is breaking delivery (of email). I mean, sure, replace the headers and mail body with a link to your gopher site or something. But at that point, you're not really delivering email anymore.
Yeah, and it's not really email either. Facebook started doing something similar for its "email notifications" a good while back. At one point, they sent the comment body in the email notification alerting you to a new comment - so you didn't have to use the (Web) app just to read a couple of lines of text. So they used to have email integration. These days they've settled for email annoyance.
Even with the first, Google supports forwarding all mail to an arbitrary email address, which means the "Gmail" becomes a text-file stored on a dovecot server (or other regular mail server) somewhere.
So unless they break delivery (you can forward only some subset of emails) - there's no way for the sender to have any better guarantee than "please delete after reading".
At least the pgp spec has (had?) an "eyes only" flag that, while it didn't guarantee anything, at least meant compliant software would try hard to not leave a plain text copy on the filesystem.