> In IMAP, a client is free to cache any part of a message for as long as it > wants. That implies that once a server has sent e.g. a message's ENVELOPE > to a client, that message can't be changed any more, or the client's cache > would hold incorrect data.
It implies nothing of the sort. A client's decision to cache any part of a message for eternity is purely on the shoulders of the client. It has no bearing on how the server should store the data. Again, think of a browser. I could set the caching such that the first time I visit a web site, that web page is cached forever, but I claim that wouldn't be very useful. > The only way for a server to invalidate the client's cache is to send an > EXPUNGE for the relevant message and issue a new UID. With current clients, I absolutely agree. But, as I mentioned into another reply, I think enabling updates for current clients is not necessary. What is necessary is that they don't break. Newer clients will be able to make use of an update capability. JM
