You know the term "opinionated software"? IMAP is an opinionated protocol, designed for clients and servers that work exactly the same way that Mark Crispin's PINE and UW-IMAPd did. Disagree with Crispin about anything, and the protocol will fight you every step of the way.

Mind you, I think PINE may have been the greatest email program ever written, but Crispin was not the easiest person to get along with.