[robryk]

As with race conditions, making things faster doesn't change things but only exposes preexisting problems. The preexisting problem I see here is sloppy definition of existence for the message: if you can see the message on a burning piece of paper, it should be considered to still exist (just as a message being sent with smoke signals does not disappear the moment it's committed to smoke).

E: The obvious way to fix this is to stop talking about messages existing/not existing, but talk in terms of messages being stored in X (or having been deleted from X), for some value of X.

[alpinisme]

It’s not the word “exists” that causes the problem (although it definitely gives it an added air of strange mystery). It’s the word “this.” Consider the case of a draft email I am writing on my laptop, but have to leave before finishing. Later, I resume composing the email on my phone and I hit send. But I do it in a hurry and mostly forget about it. The next morning, though, I open my laptop and I see the still unfinished draft I left there.

Now, when I try to finish and send that I’m hopefully going to get an error message. But “you already sent this email” is both right and wrong, since “this” email (the one I’m looking at) may have different contents from the one I sent.

Agreed that the best error message is just more precise though: “You are attempting to edit a draft that you already finished and sent from another device. Would you like to treat this as a new email?” Or something like that.