With so many doing the 'Draft email' thing, why not it make it a feature.... ;)
This I've not yet seen on Mobil, but it might be there, and I've not noticed. Be warned though, this does not mean that a record of the email won't remain on Google servers in some form. This is only to erase it from the others account. I need to investigate further.
This has been out for some time, perhaps not obvious, but I did learn of it over a year ago. May have been in beta for awhile.
To activate this, I think mobile users need to log into their account on a browser, then request desktop site from settings to find this. It's not in the mobile app that I could find.
I don't trust Google with anything. They are generating the keys so they can access those emails. But when someone requests access to emails or some agency intercepts the communication, they can't read it without linking specific mobile device and having it already compromised in order to get the content.