How IMAP works under the hood

Interesting no attempt has been made to make it at least be less heavy on networked bytes. Especially since it is old and was meant to be used on a connection with no compression or encryption.

HasChildren could have been Parent, HasNoChildren could have been Leaf or Child. And so many more things.

The protocol has ossified and been entrenched. In general more efficient usage of IMAP relies on extensions to the protocol.

A modern replacement (JMAP) hasn't been adopted by major providers.

If you really cared about data transfer size you'd use something like Protobuf.