I've posted a similar question on the comp.mail.imap newsgroup but maybe someone here can answer the question.
What are the IMAP subscribe and unsubscribe functions for? I don't mean what do they actually do in any particular mail client, I mean what is their intended purpose and use?
I can find nowhere that offers a good overall description of IMAP and how it's supposed to work even after spending quite a while Googling. There's the RFC of course but that's hardly user (or even techie) friendly. Apart from that there are lots of descriptions of specific server and client implementations but since they all differ in quite significant ways in the way they handle subscribe/unsubscribe they don't really help a great deal.