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).

> But nobody does that, everyone leaves their mail on the server.

Absolutely not. I have a personal e-mail address which is IMAP and a shared mailbox with my wife which is POP (I don't want my mail read if she reads it). Mail clients are configured to leave mail on the server for 1 month. It's not complicated.

I for one use pop3 and am really content with it. I cannot bear the idea of keeping my personal mails on a remote server. And that of having to use a web interface to configure splitting rules via a web interface, unable to easily version control and undestructibly and easily test.

You seem to have a personal (!) problem with POP3. Why is that? Are you forbidden to use IMAP because of it? Are you forced to implement a POP3 server?

Whoo-hoo! I'm a nobody!

No, it's highly inefficient in the face of latency, because there essentially is no batch fetching primitive. Fetching messages over a high latency connection (e.g. to a server on the other side of Earth) takes forever if you have a lot of messages.