President Dwight D. Eisenhower established the Advanced Research Projects Agency in 1958, recruiting scientists to design the first large-scale computer network, which was intended to support the American military during the Cold War. Academics would use the network to communicate with one another via email between several US research universities.
I mean you know that the Internet is nowadays instantaneous because accessing websites, instant messaging, online phone calls, etc. are instantaneous …
Email isn’t really intended to be used as an instant messaging system. A lot of the time, email clients are configured to only check for new emails periodically. Email servers might be configured to have some delay to avoid using too many resources at once. At least for me, emails (e.g. password reminder emails) do usually arrive within a few seconds, but indeed not always as immediately as instant messages.