How IMAP works under the hood

That was a pretty interesting read. I didn't realize one could interact directly with an IMAP server like we can with FTP and telnet + HTTP.

POP is a little simpler, but IMAP is designed for concurrent access by multiple clients to the same account.

What this article doesn't address is OAUTH, which is required more often now.

That's a hugely important use case, especially nowadays. People have mail clients running at the same time from multiple devices; e.g. desktop and mobile. Also multiple browser tabs with an instance of their webmail.