Here is a patch to add some support for read-only IMAP folders.
   This is most useful if you have multiple copies of mutt open, but
   it also allows you to open a folder read-only and not have to
   worry about flags getting changed. Toggling read-only still
   doesn't work correctly - you may lose your 'N' flags if you open
   a folder normally and switch to read-only.

  I've also decided to try using UID FETCH, although I'm not sure if
  older IMAP servers support it, but then again I'm not sure if
  anyone's using any really old IMAP servers. The main advantage is
  in the case of multiple clients, where one client is deleting
  messages and the other isn't getting notification. I'm
  experiencing that on my UW-IMAP 4.6 server. On the other hand,
  this server seems to have all sorts of terrible problems with this
  scenario, so I'm not sure how well the code functions. It's a
  two-line change so far, it's experimental, and it's the only IMAP
  code in an #if 0 block...