                            Courier-IMAP version 4.0

   Contents of this NEWS file:

     Introduction
     Shared folders and access control lists

  Introduction

   Courier-IMAP 4.0 brings many changes and improvements. All
   authentication-related code in Courier-IMAP has been moved into the
   external Courier Authentication Library. See the contents of the INSTALL
   file for more information. Courier-IMAP now includes an IMAP/POP3
   aggregation proxy, like Perdition. See the "imap/README.proxy" file in the
   source distribution for more information. Mail accounts can be distributed
   across a pool of servers. A separate server (or another pool of servers)
   accept connections from IMAP and POP3 clients, waits for the client's
   login request, looks the mail account's server, and connects to the
   IMAP/POP3 server on the right host, with the IMAP/POP3 client being no
   wiser. Any kind of an upper limit on the scalability of the IMAP/POP3
   server, or how large of a mail store it can support, has been eliminated.
   The only limit to Courier-IMAP's horizontal scaling is the available
   bandwidth on the LAN.

  Shared folders and access control lists

   New to Courier-IMAP 3 are the ACL (access control list) IMAP extension,
   and ACL-based virtual shared folders. Courier-IMAP 3 implements both the
   existing ACL specification, RFC 2086, as well as an experimental
   implementation of the second draft revision of the ACL specification.
   Virtual shared folders is a different implementation of shared folders
   that supplements an older implementation in Courier-IMAP 2, and earlier.
   The older, POSIX permission-based shared folders are still implemented and
   supported. Here's a summary of the differences between the two shared
   folder mechanisms:

      POSIX-based shared folders              ACL shared folders
                                  May be used with virtual accounts only;
     May be used with system      cannot be used on systems that have
     accounts only^1              end-user login shell access: bypassing ACLs
                                  and accessing the folders directly is
                                  trivial
     Access rights based on       Access rights based on IMAP access control
     traditional POSIX filesystem lists
     permissions
     Sharable folders must be set A site-specific process must be installed
     up manually, using the       to compile an index of all virtual
     "maildirmake" command        mailboxes; afterwords, individual users may
                                  create and manage shared folders themselves

       ^1 This is because access rights are governed by filesystem
       permissions. POSIX shared folders may also be used with virtual
       accounts, but it will not be possible to grant read-only access to
       shared folders, and everyone will be able to delete messages from
       shared folders (instead of only the creator of each message)

   After installation, read the "maildiracl" manual page for a brief overview
   of access control lists.

   Read "maildir/README.sharedfolders.html" for information on configuring
   virtual shared folders
