Earlier quoted context omitted.
Why is POP3 horribly inefficient? Lack of an equivalent to the IMAP COMPRESS extension?
POP3 is only efficient if you download all mail to the client and immediately remove it from the server. But nobody does that, everyone leaves their mail on the server. Then everytime you synchronize the server has to go through all the mail it has to see what you don’t have, which is very inefficient if you have 10000 mails in your inbox, like most people have these days. It’s optimized for a usecase that doesn’t ex…
I don't think it is at all fair to call POP3 inefficient on this basis. It is fine if you use it in the way it is intended (and presumably optimised) for. It was designed as a delivery mechanism back when people didn't tend to have permanent connections and space on servers wasn't cheap. Users wanted mail locally for disconnected use and servers wanted rid of it once delivered onward.
Where it is not the right tool for the job, use the tool that is instead (IMAP presumably in this case).