Since the introduction of iOS 16, Apple has a new feature called Undo Send Delay.
Unfortunately, there's a bug affecting some users where this new feature prevents some of your email from sending, and also from being recorded in your Sent folder.
Because the email doesn't even make it to our servers, it's as if you never sent the email at all, despite hearing the familiar swoosh indicating the email was sent.
If you want to be sure to avoid this issue, or to resolve it in the event it's affecting you, then turn off Undo Sent Delay.
The feature can be found at the bottom of your Settings > Mail page.
Thursday, August 3, 2023