Nothing on the internet is guaranteed. Everything is at some point a leaky abstraction. While it's possible for a mail to just disappear (or more often, automa

Nothing on the internet is guaranteed. Everything is at some point a leaky abstraction. While it's possible for a mail to just disappear (or more often, automatically be sorted into a spam folder) the protocol is designed to be quite robust in how responsibilities for delivery are passed on to servers delivering the message.