Fair enough, Lawrence, although I'm not sure that ordinary users would ever need or encounter such a thing, much less suffer consequences ... and anyway, the thread is about "emails not sending". This everyday problem is solved in a few taps to switch off "Delay Sending" in Mail Settings. That's it.
Hey Apple, if you must make this "feature" the default when it previously never existed (which is extremely confusing: stuff that previously just worked - remember those days?) then at least pop-up a warning like "Email will send in 10 seconds - withdraw?" and defo let the countdown run in the background, even if the app is closed, or perhaps put the email in the Outbox until it sends so that we have some visibility of what's going on - and ffs do not reassure us with the "woosh" we hear that confirms an email is sent when it's in fact still counting down ... to infinity if you close the app before the clock is run out!
Arghhhhh, Apple doesn't fix the things we really want and complain about a lot (sensible meeting invite confirms in Calendar to *all* systems, even if they're Microsoft, so that we can work simply and effectively), but they add useless stuff nobody asked for - and then in a user-unfriendly, undo-working-systems that we've used hundreds of times per day for over a decade, and in a hopelessly confusing way.
Listen to your users, Apple!