Add support for more folder properties. MAPI uses:
PidTagContentCount - number of messages in a folder
PidTagContentUnreadCount - number of unread messages
PidTagFolderId - FID structure (?) / PidTagParentEntryId
PidTagSubfolders - bool indicating subfolders existance
PidTagLocalCommitTime - datetime of last change (there's no such thing in IMAP?)
PidTagAttributeHidden - can we use subscription here?
PidTagComment - imap annotations?
PidTagCreationTime - imap annotations?
there are others, but they might be hard to implement (reasonably), e.g. cumulative size of messages in a folder or folder hierarchy change indicator (an integer that increases on every subfolder addition/deletion).