I’m trying to think of a situation when as the sender you want to do this. Because it is the benefit of written communications is that the content can be re-used.
Even if you were sending something to someone where you wanted them to read it, memorize it, and destroy it like in some spy TV show/movie, there is the possibly that it could be opened but not gotten a chance to actually read it, and they never end up seeing the message.
As an aside, it is possible to create a file that’s a valid program on multiple different systems. I’ve seen a file that was valid source code for “Hello World” in (IIRC) Basic, C, Fortran, and Bash script, and the file itself was also a valid x86 compiled .com file. Mostly, this was based on clever use of characters that would be interpreted as comments in some languages but not others.
The IETF doesn’t have that kind of power, and nobody else does, either. Not in the general case, where we’re talking about, as you are, email as an interoperable standard which can be sent and received between multiple kinds of computer and device using software written by multiple entities.
The geeks would rightly say that cancelling email is no more enforceable, at a technical level, than cancelling Usenet news, a few would wonder if the IETF had finally gone nuts, and everything would be forgotten, unimplemented, in a few months.
As others have said, if you control the entire pipeline, and nobody tries to subvert it, you can make it work. You can say much the same about a bank vault with doors that don’t lock.
The internal messages weren’t links to something else. They popped up, and if the sender set the controls a certain way, that message would disappear when the recipient closed it instead of being saved to the recipient’s account like would normally happen. But I guess that still is not the same thing. Seems like there could be a way to do that though.
On an internal messaging system, you (well, your IT group) controls both email clients, all intermediate systems, and what they all do does. In general email, you only control your email client, not intermediate systems or the other person’s client. So it’s not actually ‘more difficult’, it’s completely impossible - the other person’s mail server might save a copy of every message that goes through it, and you can’t stop that. Their email client might not honor (or even understand) your delete request, or
might do a regular delete of the email (which puts it in the trash folder, where it can be recovered) or might automatically save a copy of every message. Even if you force them to use a client that you control that connects to a server you control, they could simply screenshot the message or physically record the video output from the PC to the monitor.
Also, did your internal messaging system prevent you from cut and pasting from the email, or from taking a screenshot of the message? Or somehow prevent you from snapping a pic of the monitor with a camera that’s not part of the computer? Because it probably wasn’t as secure as you think it was.
I’m sure. But there were a lot of old dinosaurs there like me. I’ve only recently learned how to take a screenshot in the first place.