
                                 Courier-IMAP
                                       
   For a general introduction and configuration settings for some popular
   IMAP clients, go and read imap/README(.html).
   
   In this document:
     * Upgrading
     * Installation
     * Authentication modules - General notes
     * Authentication internals
     * USERDB Authentication module
     * VCHKPW Authentication module
     * LDAP Authentication module
     * DAEMON Authentication module
     * Using shared folders
     * CRAM-MD5 Authentication
       
UPGRADING

   If you are upgrading from a previous install of Courier-IMAP you
   should back up the contents of your configuration directory before
   starting the upgrade. The default configuration directory is
   /usr/lib/courier-imap/etc. The installation procedure installs a fresh
   set of default configuration files, overwriting the existing ones.
   
   New releases usually introduce additional options and features that
   must be configured. Keeping old configuration files in place means
   that it's very likely that things will not work after an upgrade,
   because some required option has not been set. The safest approach is
   to always install a fresh set of default configuration files, each
   time. Then use your backed up configuration directory to reset your
   required configuration.
   
   The recommended upgrade procedure is as follows:
     * Back up /usr/lib/courier-imap/etc
     * rm -rf /usr/lib/courier-imap/br>
     * Follow the installation procedures, below
     * Reset your local configuration, based on the contents of backed up
       configuration files
       
   All configuration files are kept in the configuration directory.
   Nothing else in /usr/lib/courier-imap is configurable.
   
INSTALLATION

   To compile and install the Courier-IMAP server (the short version, a
   longer version follows):

$ ./configure [ options, see below ]
$ make
$ make check       # Note - the --enable-workarounds-for-imap-client-bugs
                   # option to configure will result in make check FAILING.
$ su root
# make install     # Or, make install-strip, to strip the executables

     NOTE
     
     You MUST run the configure script as normal user, not root. Did you
     extract the tarball as root? It won't work. Remove the extracted
     source code. Log in as a normal user. Extract the source code as a
     normal user, then run configure. You will do everything as a normal
     user, except for the final step of installing the compiled
     software.
     
   NOTE: The configure script may run as much as 5-10 minutes on slow
   machines. It may appear that configure is stuck in a loop, but that's
   an illusion. Courier-IMAP is built from a collection of modular code
   libraries, each with its own configuration script. The configuration
   scripts share a lot of common code, leading to an initial impression
   that the same configuration script is being repeatedly run.
   
   You should try make install-strip first. Use make install if make
   install-strip fails.
   
   The configure script accepts certain options, but the defaults should
   be fine most of the time. make install puts everything in
   /usr/lib/courier-imap. If the directory /etc/pam.d exists, make
   install creates /etc/pam.d/imap, obliterating any existing file of
   that name. If you have some other IMAP server installed, this means
   that you will want to save your existing configuration in
   /etc/pam.d/imap.
   
   "make check" performs some internal sanity checks. If make check
   fails, something is wrong, and Courier-IMAP may not work for you
   reliably.
   
   After installation, you will need to review
   /usr/lib/courier-imap/etc/imapd.config and make any changes you deem
   necessary, including:
     * If you do not want to create and use virtual mailboxes, you should
       remove authuserdb from AUTHMODULES. If AUTHMODULES contains
       "authdaemon", you will have another configuration file,
       authdaemonrc. Remove authuserdb from authdaemonrc instead.
     * The configuration script automatically selects whatever
       authentication modules can be used on your system, but you may not
       necessarily want to use them. For example, if your system has
       OpenLDAP libraries installed, the authldap module gets compiled
       and installed, even though you might use LDAP for some other
       purposes, and not necessarily authentication. If that's the case,
       remove authldap from the AUTHMODULES entry in imapd.config, or
       from authdaemonrc, whatever the case might be.
     * If you're using PAM authentication (authpam gets compiled and
       installed), you will have to tell your PAM library how to
       authenticate the "imap" service. What you need to tell your PAM
       library is something that you will have to figure out by yourself,
       because it depends on the version of your PAM library, and your
       operating system.
       If the directory /etc/pam.d exists, the installation script will
       automatically install /etc/pam.d/imap, but that's just the start
       of it. You will still have to inspect its contents and adjust the
       full pathname to the PAM modules, if necessary.
       Some versions of the PAM library, do not use the /etc/pam.d
       directory. Instead they use a single configuration file
       /etc/pam.conf. Here's an example of what needs to be added to
       /etc/pam.conf on FreeBSD 4.0. NOTE: other platforms may need
       something similar:
imap  auth    required        pam_unix.so      try_first_pass
imap  account required        pam_unix.so
imap  session required        pam_permit.so
       Your PAM library may use pam_pwdb.so instead of pam_unix.so;
       consult the documentation for your PAM library for more
       information.
       
   configure should automatically detect if you use vpopmail, and compile
   and install the authvchkpw authentication module.
   
   After running make install or make install-strip you will then have to
   modify your system's startup scripts to run Courier-IMAP when your
   system boots.
   
   Use the following command to start the Courier-IMAP server:

$ /usr/lib/courier-imap/libexec/imapd.rc start

   This assumes that Courier-IMAP is installed in /usr/lib/courier-imap.
   Use the following command to stop Courier-IMAP:

$ /usr/lib/courier-imap/libexec/imapd.rc stop

   You will have to add these commands to your system startup/shutdown
   scripts.
   
    IMAP over SSL
    
   To add SSL support you have to install OpenSSL before installing
   Courier-IMAP. Download OpenSSL from http://www.openssl.org/. Follow
   the instruction in OpenSSL package to install it and configure it. SSL
   support in Courier-IMAP has been tested with OpenSSL 0.9.5a.
   
   The /usr/lib/courier-imap/lib/imapd-ssl.config configuration file sets
   some additional options for SSL, which you may need to adjust. Consult
   that configuration file for additional information. Then, you also
   have to run the /usr/lib/courier-imap/libexec/imapd-ssl.rc script from
   your system startup and shutdown scripts, just like the
   /usr/lib/courier-imap/libexec/imapd.rc script. You may accept both SSL
   and non-SSL connections by running both scripts.
   
   Note that SSL requires a valid, signed, X.509 certificate to be
   installed where Courier-IMAP expects to find it. The default location
   for the X.509 certificate, in PEM format, is
   /usr/lib/courier-imap/share/imapd.pem. The X.509 certificate must be
   signed by a certificate authority that is known to the IMAP client.
   You can generate your own self-signed certificate by running the
   script /usr/lib/courier-imap/share/mkimapdcert which will work too,
   except that IMAP clients using SSL will display a warning message the
   first time they connect to the server. To get rid of the warning
   message you'll have to pay for a signed X.509 certificate. The gory
   details of setting up SSL is beyond the scope of this document, and
   you should consult the OpenSSL documentation for more information.
   
   The mkimapdcert script will not overwrite an existing imapd.pem
   certificate, in order to allow precompiled packages to simply call
   mkimapdcert after installation, without worry.
   
    System-V style startup
    
   If your system uses System-V style startup scripts, here's a sample
   script you can install in /etc/rc.d/init.d:

#!/bin/sh
#
# courier-IMAP - IMAP server
#
#

case "$1" in
start)
        cd /
        . /usr/lib/courier-imap/etc/imapd.config
        echo -n "Starting Courier-IMAP server:"
        case x$IMAPDSTART in
        x[yY]*)
                /usr/lib/courier-imap/libexec/imapd.rc start
                ;;
        esac

        . /usr/lib/courier-imap/etc/imapd-ssl.config
        case x$IMAPDSSLSTART in
        x[yY]*)
                test -x $COURIERTLS && \
                        /usr/lib/courier-imap/libexec/imapd-ssl.rc start
                ;;
        esac

        echo " imaplogin"
        ;;
stop)
        echo -n "Stopping Courier-IMAP server:"
        /usr/lib/courier-imap/libexec/imapd.rc stop
        /usr/lib/courier-imap/libexec/imapd-ssl.rc stop
        echo " imaplogin"
        ;;
restart)
        $0 stop
        $0 start
        ;;
esac
exit 0

   Then, create a soft link to /etc/rc.d/init.d from the run-level
   subdirectories underneath /etc/rc.d.
   
    Options to configure:
    
     * --prefix=pathname - install here, instead of /usr/lib/courier-imap
     * --without-ipv6 - do not compile IPv6 support. The configure
       automatically checks if IPv6 support is available, and enables it
       automatically. This option suppresses IPv6 support, even if it's
       available. IPv6 support means that Courier-IMAP will create an
       IPv6 socket and accept IPv6 connections. --without-ipv6 should be
       used if your system does not fully support IPv6, or if its
       implementation is buggy. Most Linux distributions now ship with
       IPv6 support in glibc, but without compiling the kernel for IPv6
       support. This results in modprobe regularly complaining in
       /var/log/messages about the fact that it can't load the IPv6
       module. Use --without-ipv6 to turn off IPv6 support, if that
       bothers you.
     * --with-module, --without-module - explicitly specify that the
       authentication module named "module" should be included or
       excluded. See below for more details.
     * --bindir=pathname, --mandir=pathname - override default names of
       subdirectories under prefix. See below for more information.
     * --with-db=db - Use the DB library instead of the GDBM library You
       must have either the GDBM or the DB library installed. If both are
       present, GDBM is selected unless you use this option. The GDBM/DB
       library is used by Courier for certain functions.
     * --with-piddir=dir - use dir/imapd.pid to store couriertcpd's
       process ID.
     * --with-userdb=file - use file instead of /etc/userdb (also means
       that userdb.dat and userdbshadow.dat are appropriately renamed).
     * --enable-workarounds-for-imap-client-bugs - there are a number of
       various bugs in certain IMAP clients. The current list of broken
       IMAP clients consists of Netscape Messenger and Sun's StarOffice.
       This option enables some workarounds for some bugs in these
       clients, however, note that this may break compatibility with
       software that correctly implements IMAP4rev1. Additionally, "make
       check" will fail when this option is used. See
       imap/BUGS.(html|txt) for more information. NOTE - if this option
       is used, make check WILL FAIL. You should first configure
       Courier-IMAP without this option, run make check, then reconfigure
       Courier-IMAP with this option.
       
    Installation directories
    
   Unless the options --prefix, --bindir, or --mandir are specified,
   everything will be installed in the directory /usr/lib/courier-imap.
   
   Use the --prefix option to specify a different directory. This
   directory will contain the following subdirectories:
     * etc - configuration files
     * bin - binaries
     * sbin - superuser binaries
     * libexec - additional binaries
     * man - manual pages
     * var - temporary files used by the authdaemond, daemon process (if
       the authdaemon authentication module is selected).
       
   Having everything installed underneath one directory allows its
   contents to be easily backed up, before a newer version of
   courier-imap is installed. Reverting to a previous version is as
   simple as restoring from backup.
   
   Because some binaries in bin and sbin may be executed from the command
   line, it will be necessary to change your systemwide global startup
   script to add this directory to the default PATH. Additionally, it
   will also be necessary to modify the configuration of the man(1)
   command so that it can find Courier-IMAP's manual pages in this
   directory:
        PATH="/usr/lib/courier-imap/bin:$PATH"
        if test -w /etc
        then
                PATH="/usr/lib/courier-imap/sbin:$PATH"
        fi
        export PATH
        MANPATH="/usr/lib/courier-imap/man:$MANPATH"
        export MANPATH

   As an alternative, you may use the --bindir and --mandir options in
   order to install binaries to /usr/local/bin and the manual pages to
   /usr/local/man, which should already be searched by default:
        ./configure --bindir=/usr/local/bin --mandir=/usr/local/man

AUTHENTICATION MODULES - GENERAL NOTES

   Authentication modules are responsible for taking the entered userid
   and password, validating them, then locating the corresponding Maildir
   for the userid.
   
   There are several authentication modules available. Each
   authentication module implements a separate way of authenticating
   logins, and not all authentication modules can be used by everyone.
   Some authentication modules can be used only on systems that have
   certain libraries or software installed separately.
   
   The configure script will attempt to pick a default set of
   authentication modules to install, but the --with-module and
   --without-module options to the configure can always specify whether a
   given authentication "module" should be explicitly included or
   excluded. Multiple --with and --without options are, of course,
   allowed (each one specifying a different authentication module). As
   explained later, it will not be necessary, in most cases, to
   explicitly specify the disposition of each one of the following
   authentication modules, and most people will find it sufficient to let
   the configure script decide which one of the following authentication
   modules are required:
     * authpwd - this module looks up userids and passwords in your
       /etc/passwd file, or the equivalent NIS map (as supported by your
       system's getpw library).
     * authshadow - this module is like authpwd, except that it should be
       used on systems that use shadow password files, /etc/shadow.
     * authpam - this module should be used on systems that have the PAM
       library. With this module, Courier-IMAP will use whatever PAM
       modules you specify for authenticating the "imap" PAM service.
       Essentially, authpam allows any PAM module to be used for
       authenticating logins. NOTE: in addition to including this module,
       you will have to take additional, site-specific, steps in order to
       configure your PAM library for the "map" PAM service. The specific
       details regarding your PAM configuration differs from system to
       system, and you should consult your own documentation. It might be
       tempting to throw in a towel and use authshadow or authpwd if you
       cannot figure out how to install PAM support, however that is not
       advisable. It is highly recommended to use authpam wherever the
       PAM library is available.
     * authuserdb - this module uses GDBM or DB database files, usually
       /etc/userdb.dat and /etc/userdbshadow.dat to look up userids and
       passwords. These files are GDBM or DB databases that are loosely
       equivalent in function to /etc/passwd and /etc/shadow. These
       databases are maintained indirectly by several Perl scripts, which
       build these database files from a plain text file, usually called
       /etc/userdb. This file can be modified by any text editor, or it
       can be managed by some useful Perl scripts which are included.
       /etc/userdb may also be a subdirectory that has multiple text
       files in the same format, which are simply concatenated. userdb
       allows creation of virtual mail accounts that do not have a
       corresponding login account -- virtual mail accounts that can
       share the same, reserved, system userid. /etc/userdb can also be
       used to complete supersede /etc/passwd. With many accounts it can
       be quite a drain to have to continuously linearly scan /etc/passwd
       in order to look up an account. Instead, a fast database lookup
       can retrieve the same information from the database file. Read the
       included manual pages, starting with userdb(8) for more
       information.
     * authcram - this module is similar to authuserdb (it uses the same
       databases), but implements CRAM-MD5 authentication. See below for
       more information.
     * authmysql - native MySQL authentication module
     * authvchkpw - this is another virtual mail database lookup module,
       except that it uses the vpopmail vpasswd files. This module is
       provided for a quick way to use your existing vpopmail vpasswd
       files. Where possible, you should convert over to /etc/userdb. The
       included script vchkpw2userdb(8) might be of some help in doing
       so.
     * authldap - authenticates against an LDAP server. This is a new
       module included with Courier-IMAP. See below for more information.
     * authmysql - native MySQL authentication module authpwd. Beta -
       read authlib/README.authmysql for information on how to set up
       this module.
     * authdaemon - daemon authentication proxy. See below for more
       information.
       
   It is possible to include more than one authentication module. For
   example, if you select both authuserdb and authpam, each login will
   first be authenticated against /etc/userdb. If Courier-IMAP cannot
   find the account in /etc/userdb, it will then attempt to authenticate
   using the PAM library.
   
   If neither --with nor --without is specified for any one of these
   modules, the configure script will try to figure out whether or not to
   the given authentication module should be used. Therefore, in most
   situations, it will not be necessary for you to explicitly specify
   what to do with each authentication module. For most people, letting
   configure figure it out will be sufficient.
   
   configure will use the following logic to determine which
   authentication modules need to be included by default:
     * authuserdb - this module is always included by default
     * authpam - configure will attempt to detect if the PAM library is
       installed, or not. In most cases an explicit --with-authpam will
       not work if the PAM library is missing, because PAM development
       libraries, required for compilation, are probably unavailable as
       well. --without-authpam can be used to avoid installing authpam on
       systems that do have a PAM library installed. Hopefully, you will
       have a good reason to do something this silly.
     * authldap - configure will attempt to detect of the LDAP library is
       installed, or not. If the LDAP library is available, authldap will
       be compiled and installed.
     * authpwd, authshadow - whether or not these modules are installed
       by default depends upon what happened with authpam and authldap.
       If PAM or LDAP support is installed, via authpam or authldap,
       these two modules are usually not necessary, because the PAM
       library, or the LDAP server, provides this functionality. If PAM
       support is unavailable, these modules will be installed by
       default.
     * authvchkpw - this module is compiled by default only if the
       vpopmail account is defined.
     * authmysql - this module is compiled if MySQL client libraries are
       available.
       
Confirming selected authentication options

   You can find out what authentication modules were actually used, but
   you must first run make successfully. Running make compiles the
   authinfo program in the authlib subdirectory. This program tells you
   what authentication modules were compiled.
   
USERDB AUTHENTICATION MODULE

   userdb is a way to implement many virtual mailboxes - many mailboxes
   that do not have to have a separate system userid allocated for each
   one, and there is no system login associated with each mailbox. userdb
   uses a database for mapping virtual addresses to physical maildirs. It
   should be scalable to thousands of mailboxes. It can also be used to
   replace linear searches of /etc/passwd with a database lookup, see
   pw2userdb(8).
   
   This is a rough overview of using userdb. For additional information,
   read makeuserdb(8), and userdb(8). All the scripts will be installed
   in /usr/lib/courier-imap, so look for them there.
   
   Courier-IMAP can use the userdb database simply by the virtue of
   installing the authuserdb authentication module, which happens by
   default. The tricky part is creating the database. Hopefully, it's
   only tricky once, and the second time it won't be so tricky any more.
   The userdb configuration is extremely flexible, and there are many
   ways of actually setting up the database.
   
   The best way to describe how userdb works is to try to create one
   virtual mail account, let's call it vmail.
   
  Simple userdb setup.
  
   This approach should be used if you do not have many virtual
   mailboxes. It's very simple, but quickly becomes cumbersome if you
   administer many virtual mailboxes.
   
   Create an empty /etc/userdb.

# cp /dev/null /etc/userdb
# chmod 700 /etc/userdb

   /etc/userdb must have 700 permissions.
   
   Now, run the script pw2userdb. This script converts the contents of
   your /etc/passwd to the /etc/userdb format (including the contents of
   /etc/shadow, this is why permissions on /etc/userdb must be 700). This
   script is usually used where you want to convert a very large
   /etc/passwd to /etc/userdb. userdb applications can now use a fast
   userdb database instead of a linear scan of /etc/passwd in order to
   look up system accounts. However, you probably don't want to do use
   this feature right now, so what you simply want to do is take the
   output of pw2userdb, and find the entry for the vmail account that you
   created earlier. Look for a line that starts with 'vmail' followed by
   tab, followed by familiar fields from /etc/passwd. Save the output of
   pw2userdb in a temporary file, edit it, and remove everything except
   the line containing vmail, and the very next line, which is a special
   entry that maps vmail's userid back to the vmail record.
   
   Here's what you might find in the output of pw2userdb:

vmail   uid=1012|gid=1012|home=/home/vmail|systempw=*
1012=   vmail

   The actual numerical values and the home directory location may vary.
   Save these two lines as /etc/userdb, and set the permissions on
   /etc/userdb to 700:

$ chmod 700 /etc/userdb

   This is a one time step only, and Courier-IMAP does not really need
   it. However, there are other applications that use /etc/userdb which
   may require it.
   
   Now, with that out of the way, let's really create a virtual account.
   In this example we'll create a virtual mailbox for 'john@example.com'.

# su vmail
$ cd $HOME
$ maildirmake Maildir-john-example
$ exit
#

   You may need to specify a full path to your maildirmake program. The
   end result is that you created $HOME/Maildir-john-example in vmail's
   account.
   
   The next step is to configure your mail server to deliver mail for
   john@example.com directly into the maildir
   ~vmail/Maildir-john-example. How that's done depends on the mail
   server that you use.
   
   Now, let's connect the dots here, and create an entry in /etc/userdb
   for john@example.com:

# userdb "john@example.com" set home=/home/vmail \
                                mail=/home/vmail/Maildir-john-example \
                                uid=UUU gid=GGG

   This command runs a Perl script named userdb , which is installed, by
   default in /usr/lib/courier-imap/sbin. Replace UUU and GGG with the
   userid and groupid of the vmail account. If you now look in
   /etc/userdb, you will see that a new record for john@example.com has
   been appended to the end of the file.
   
   We're not finished yet. We need to set the IMAP password for this
   mailbox:

# userdbpw | userdb "john@example.com" set imappw

   If you are running Red Hat Linux 6.0, or higher, you can specify the
   -md5 option to userdbpw, in order to use an MD5 password hash, instead
   of crypt. Specify "systempw" instead of "imappw" if you would like to
   use the same password with any other application that uses . The
   imappw field is only checked by Courier-IMAP. If not defined, systempw
   is used instead.
   
   Finally, compile the database:

# makeuserdb

   This command creates the actual database, /etc/userdb.dat and
   /etc/userdbshadow.dat from the plain text file /etc/userdb.
   Courier-IMAP will now start accepting logins to this mailbox. Adding
   and removing mailboxes can be done while Courier-IMAP is running.
   
   Courier-IMAP reads /etc/userdb.dat and /etc/userdbshadow.dat only. The
   plain text source, /etc/userdb is not read by Courier-IMAP itself.
   Changes take effect only when makeuserdb runs.
   
  Large virtual domain farm.
  
   The previous approach uses a single flat file, /etc/userdb. This might
   be a bit cumbersome if you have thousands of virtual mailboxes in many
   domains. Here's an alternative approach that can scale to thousands of
   domains and mailboxes.
   
   Instead of creating /etc/userdb file, make it a subdirectory:

# mkdir /etc/userdb
# chmod 700 /etc/userdb

   Now, create /etc/userdb/default, containing pw2userdb's output for the
   vmail account, as previously described.
   
   This time, you probably want to create all mailboxes for the same
   domain in a separate subdirectory:

# su vmail
$ cd $HOME
$ mkdir -p domains/example-com
$ maildirmake domains/example-com/john
$ exit

   The idea is that all the maildirs for @example.com will be stored in
   ~vmail/domains/example-com. All maildirs for domain.org will be stored
   in ~vmail/domains/domain.org. The actual layout and naming conventions
   are entirely up to you to define.
   
   Now, configure your mail server to deliver mail for john@example.com
   into this maildir.
   
   Here's how configure /etc/userdb.

$ userdb "example-com/john@example.com" set home=/home/vmail \
                                mail=/home/vmail/domains/example-com/john \
                                uid=UUU gid=GGG

   This creates the file /etc/userdb/example-com (the first parameter to
   the userdb command), and appends a record named "john@example.com".
   You will store all userdb entries for @example.com in the file
   /etc/userdb/example-com. All entries for @domain.org will be
   maintained in /etc/userdb/domain-org, and so on.

$ userdbpw | userdb "example-com/john@example.com" set imappw

   This sets the IMAP access password for this account. Finally:

$ makeuserdb

VCHKPW AUTHENTICATION MODULE

   This authentication module is provided for legacy support. New
   installs should use the authuserdb module. It is possible to convert
   vpopmail/vchkpw single userid authentication passwd files to
   /etc/userdb using the vchkpw2userdb script. See vchkpw2userdb(8) for
   more information.
   
LDAP AUTHENTICATION MODULE

   This module attempts to authenticate against an LDAP server. This
   option installs a sample configuration file, which is
   /usr/lib/courier-imap/etc/authldaprc by default. You will need to edit
   this file in order to configure LDAP authentication. This
   configuration file defines the location of your LDAP server, as well
   as the names of attributes used to perform LDAP authentication. See
   the comments in the sample configuration file, and the authldap(8)
   manual page, for more information.
   
DAEMON AUTHENTICATION MODULE

   The "authdaemond" process is started and stopped by the imapd.rc and
   imapd-ssl.rc script.
   
   The authdaemon module (and the authdaemond process that goes with it)
   offers an alternative to compiling all the authentication methods as
   standalone modules. Enabling authdaemon in addition to any other
   modules will result in authdaemon being built as the only "official"
   authentication module, with the other modules compiled into a separate
   process, "authdaemond".
   
   Certain authentication modules -- such as authldap and authmysql --
   connect to an external database in order to valid an authentication
   request. The database connection is comparatively expensive, and with
   a large number of connections and authentications it is much better to
   have a single daemon process running in a background, with a
   semi-permanent connection to the database, handling authentication
   requests. That's exactly what authdaemond does.
   
   The authdaemon authentication module takes an authentication request,
   and forwards it to the permanently running authdaemond daemon process,
   waits for the result, and returns the result to the application. The
   application "sees" only the authdaemon authentication module, which
   handles every authentication request and passes it along to the
   authdaemond for processing, where all the real authentication happens.
   
   The /usr/lib/courier-imap/etc/authdaemonrc configuration file sets
   several parameters for the authdaemond process. See the comments in
   the default file installed for more information. Currently,
   authdaemonrc sets two parameters: number of daemon processes, and
   which available authentication modules will be used.
   
   Although authdaemond might be built with several authentication
   modules, not all of them may be used. This allows for a single
   authdaemond build to be made that gets installed on multiple systems
   with different authentication needs. The default module list specified
   by authdaemonrc would be a list of all the available authentication
   modules.
   
   The number of authdaemond processes is also set in this configuration
   file. The more processes that are started, the more authentication
   requests can be handled. If authdaemon does not receive an answer
   within a moderate amount of time, it will assume an authentication
   failure, and abort. Try increasing the number of processes if you
   start seeing random authentication failures. However, that should only
   be used as a stop-gap measure. If the default number of authdaemond
   processes proves to be insufficient, it is far more likely that more
   resources are needed for the server (more RAM, a faster disk, or a
   faster CPU) in the humble opinion of the author. Increasing the number
   of processes should only be used as a stop-gap measure, until a more
   thorough analysis of the bottleneck can be made.
   
   After making any changes to authdaemonrc, run the following command
   for these changes to take effect:
    /usr/lib/courier-imap/libexec/authlib/authdaemond restart

USING SHARED FOLDERS

   Courier-IMAP supports shared folders. See the file
   README.sharedfolders.html for information on how to set up shared
   folders.
   
CRAM-MD5 AUTHENTICATION

   CRAM-MD5 authentication allows IMAP clients to authenticate themselves
   without sending the password in clear-text over the network.
   Courier-IMAP now supports CRAM-MD5 by default, but is not enabled for
   reasons explained below. CRAM-MD5 support is implemented by the
   authcram module, with one exception - authldap should be able to
   support CRAM-MD5 authentication if the LDAP server is used to store
   clear-text passwords.
   
   To use CRAM-MD5 it is necessary to use an IMAP client that support
   CRAM-MD5 authentication, of course. That's the easy part.
   
   The problem is that it is not possible to use the system password when
   logging in using CRAM-MD5. That's because CRAM-MD5 requires the
   knowledge of the actual password, in the clear, in order to calculate
   authentication tokens (even though that the password itself is not
   sent in the clear over the network).
   
   So, implementation of CRAM-MD5 should be attempted once you are
   comfortable and understand how Courier-IMAP works in general. Here's
   an overview of this procedure:
     * Install and implement /etc/userdb, because CRAM-MD5 authentication
       uses the /etc/userdb database (but see below for LDAP-specific
       notes).
     * Figure out which accounts are going to use CRAM-MD5
       authentication. People who do not use an IMAP client that supports
       CRAM-MD5 can continue and log in with the existing system
       password. But everyone who runs a client that supports CRAM-MD5
       authentication will need a new password. Also, it will be
       necessary to set up CRAM-MD5 passwords for everyone at the same
       time. As soon as CRAM-MD5 authentication is enabled, all CRAM-MD5
       enabled clients will attempt to use it. If no password is
       available, Courier-IMAP has no choice but to reject the
       authentication attempt. Once that happens, the client will
       correctly interpret it as an authentication failure (and it is),
       and the client will not even try to authenticate using the system
       password. Use the following command to assign a CRAM-MD5 password:
userdbpw -hmac-md5 | userdb userdb set hmac-md5pw

       Then run the makeuserdb command, as always.
     * NOTE: CRAM-MD5 authentication should also be supported by the
       authldap module directly, as long as clear-text passwords are
       stored by the LDAP server. See below for more information.
       Therefore, if you use LDAP authentication, and you store
       clear-text passwords, you should all set and ready to go, and you
       do not need to install /etc/userdb, as described in this section.
       
  Enabling CRAM-MD5 authentication
  
   Because of these unfortunate complexities, CRAM-MD5 authentication is
   disabled after installation. CRAM-MD5 authentication is implemented by
   the authcram authentication module, which will be compiled and
   installed, however, Courier-IMAP will not advertise the fact that it
   supports CRAM-MD5. CRAM-MD5 authentication is also supported directly
   by the authldap module if it is configured to validate clear-text
   passwords in the LDAP database, however this feature has not been
   thoroughly tested. You do not need authcram if all you install is
   authldap (but you do need authcram if you install any other
   authentication module besides authldap, and you intend to use CRAM-MD5
   authentication).
   
   When you're ready to use CRAM-MD5, edit imapd.config and add the
   "AUTH=CRAM-MD5" keyword to the IMAP_CAPABILITY environment variable,
   then restart Courier-IMAP. There are instructions in imapd.config to
   that effect.
   
   If you do not intend to ever use CRAM-MD5 authentication, you can
   either specify --without-authcram option to the configure script, or
   simply edit imapd.config and remove authcram from the AUTHMODULES
   setting.
   
AUTHENTICATION INTERNALS

   Feel free to stop reading now, if all you want to do is install
   Courier-IMAP, without hacking it even further.
   
   It is possible to use other forms of authentication with Courier-IMAP.
   To do that, you have to write your own authentication modules.
   
   The easiest way to do that would probably be to take an existing
   authentication module, and clone it. Some documentation is available
   in the authlib subdirectory.
   
   For example, take a look at authpwd.c, which implements the
   /etc/passwd authentication. You will have to write a function that
   works something like that. The authentication function validates the
   userid/password, and sets the current userid, groupid, and current
   directory to the ones specified by the account, and calls some
   authentication library functions that do the rest of the work.
   Additionally, you will need to write a "pre-authentication" function,
   that does the same thing, but it receives only the userid, and assumes
   that the password is valid. This functionality is not actually used by
   Courier-IMAP, but it is required to be implemented within the authlib
   library framework, because authlib is used by other applications where
   this functionality is required. For authpwd.c, the corresponding
   function is implemented in preauthpwd.c.
   
   Start by cloning and re-implementing these two functions. Then, you
   need to create a two-line stub function that inserts the call to your
   function into a template for a stand-alone authentication module. Take
   a look at modauthpwd.c for an example.
   
   You will note that all authentication modules in authlib follow this
   template, which consists of three files: authfunc.c, preauthfunc.c,
   and modauthfunc.c
   
   After writing these functions, you need to add some code to
   configure.in in order to enable or disable your authentication module
   at compile time. The easiest way to do that is to simply copy the code
   that does that for one of the existing functions, and simply
   substitute the name of your own authentication function and source
   files (don't forget to append to the STATIC_LIST variable). Then,
   finally, add your code to Makefile.am. If you study Makefile.am, you
   will observe that all authentication modules follow the same pattern:
     * The source code files are always added to EXTRA_DIST, so that the
       source code is included in the distribution, in all situations.
     * The code is added to the main authentication library, libauth.a.
       The code is first added to an intermediate library, and the build
       target for libauth.a unpacks all intermediate libraries in a
       temporary subdirectory, then inserts all object modules into
       libauth.a.
     * Each authentication module also builds a .libsdep dependency file,
       that lists all system libraries that it must link with. All
       .libsdep files are used to build the libauth.dep file. The shell
       script that builds libauth.dep automatically removes duplicates.
       
   The reason that the dependency file is required is that some
   application link directly with libauth.a, instead of running a
   stand-alone authentication module -- like Courier-IMAP does -- and
   those applications need to know what external libraries they must to
   link with.
   
   A successful authentication involves initialization of a couple of
   environment variables: AUTHADDR - this environment variable should be
   set to the E-mail address that the mailbox actually represents (if
   it's a local physical address, you can leave out the domain, but
   otherwise it must be a real E-mail address); AUTHFULLNAME - the name
   of the breathing organism that reads this mailbox. That's taken care
   of automatically, if you reuse some of my code. There's no room in
   this brief README for the gory details, read the code and figure it
   out.
   
   Also note how dynamic memory allocation is handled. Also, you must
   avoid using stdio calls. Some authlib applications use the Fast-CGI
   library, which implements an incompatible set of stdio function calls.
