Installing and configuring the IMAP Server
This section describes the shell scripts to run and the configuration
files to modify once "configure" and "make" have run.
1. Create a user and group for the Cyrus subsystem. The examples in
this document assume a user of "cyrus" and a group of "mail",
though any user and group name can be used. If a user other than
"cyrus" is to be used, it must have been previously specified in
the "--with-cyrus-user=" option to "configure". If a group other
than "mail" is to be used, it must have been previously specified
in the "--with-cyrus-group=" option to "configure".
2. After you've logged in as "root", install the cyrus software.
make install
Be sure that the server programs ended up in the directory
specified by "--with-cyrus-prefix" (by default, "/usr/cyrus/bin").
3. The Cyrus IMAP server uses the 4.3BSD syslog that separates
messages into both levels and categories. Invoke "man syslog" to
see if "openlog()" takes three arguments. If it does not, replace
the system "syslogd" and "syslog.conf" with the files provided in
the "syslog" directory.
mv syslogd /etc/syslogd
mv syslog.conf /etc/syslog.conf
If you do not copy the "syslog/syslog.conf" file to the "/etc"
directory, be sure to add support for "local6.debug". The file
should include a line like:
local6.debug /var/log/imapd.log
You probably also want to log SASL messages with a line like:
auth.debug /var/log/auth.log
After installation and testing, you probably want to change the
".debug" component to something a little less verbose. Create the
log files:
touch /var/log/imapd.log /var/log/auth.log
4. Create the file "/etc/imapd.conf". Here is a sample "imapd.conf"
with a minimal number of values defined:
configdirectory: /var/imap
partition-default: /var/spool/imap
admins: curtj abell
sasl_pwcheck_method: saslauthd
For a description of all the fields in this file, see the
imapd.conf(5) man page. (Note that this file also exports values to
libsasl, the most important of them the pwcheck_method. In this
example, users are authenticated via the saslauthd daemon, which
can be run in a number of different ways.)
READ THE imapd.conf(5) MAN PAGE. There are options in there that
you will want to know about and default behavior that you may not
like.
Note that everyday users should not be administrators. Admins have
powers not granted to regular users and while the server allows
them to receive mail, some problems will occur if admins are used
as regular users. You also should not read mail as an
administrator. You should have separate accounts for reading mail
and administrating. This is especially true if using the
altnamespace option, because admins are always presented with the
standard (internal) namespace.
5. Create the configuration directory specified by the
"configdirectory" option in "imapd.conf." The configuration
directory is similar in concept to the "/usr/lib/news" directory.
It stores information about the IMAP server as a whole.
This document uses the configuration directory "/var/imap" in its
examples. This directory should be owned by the cyrus user and
group and should not permit access to other users.
cd /var
mkdir imap
chown cyrus imap
chgrp mail imap
chmod 750 imap
6. Create the default partition directories specified in the
"/etc/imapd.conf" file.
This document uses a default partition directory of
"/var/spool/imap" in the following example:
cd /var/spool
mkdir imap
chown cyrus imap
chgrp mail imap
chmod 750 imap
The partition directory is similar in concept to /var/spool/news.
It is where the mailboxes are stored. Unlike most netnews systems,
Cyrus allows you to have more than one partition.
7. If you wish to use Sieve, and you didn't configure deliver to look
in home directories (see the imapd.conf man page), create the Sieve
directory:
cd /usr
mkdir sieve
chown cyrus sieve
chgrp mail sieve
chmod 750 sieve
8. Change to the Cyrus user and use the tool "tools/mkimap" to create
the rest of the directories (subdirectories of the directories you
just created).
su cyrus
tools/mkimap
exit
If Perl is not available, it should be easy (but time consuming) to
create these directories by hand.
9. LINUX SYSTEMS USING EXT2FS ONLY: Set the user, quota, and partition
directories to update synchronously. Failure to do this may lead to
data corruption and/or loss of mail after a system crash.
Unfortunately, doing so may result in a serious performance hit. If
you are using a newer filesystem than ext2fs on Linux, this step
should not be necessary. (Running ext3 in any mode is safe.)
cd /var/imap
chattr +S user quota user/* quota/*
chattr +S /var/spool/imap /var/spool/imap/*
Also set the queue directory of the mail daemon to update
synchronously. The following example is for sendmail:
chattr +S /var/spool/mqueue
10. To enable STARTTLS support, see how to configure OpenSSL below.
11. Add the following lines to the "/etc/services" file if they aren't
already there.
pop3 110/tcp
nntp 119/tcp
imap 143/tcp
imsp 406/tcp
nntps 563/tcp
acap 674/tcp
imaps 993/tcp
pop3s 995/tcp
kpop 1109/tcp
sieve 2000/tcp
lmtp 2003/tcp
fud 4201/udp
12. Remove "/etc/[x]inetd.conf" entries. Any imap, imaps, pop3, pop3s,
kpop, lmtp and sieve lines need to be removed from
/etc/[x]inetd.conf and [x]inetd needs to be restarted.
Configuring the Master Process
1. Choose a configuration from the master/conf directory:
small.conf
bare-bones server supporting IMAP and POP
normal.conf
server supporting IMAP, POP, the SSL wrapped versions, and
the Sieve script management protocol
prefork.conf
The same configuration as above, but with some preforked
processes for faster processing.
backend-cmu.conf
Our configuration (for Murder Backend / typical IMAP
servers)
frontend-cmu.conf
Our configuration (for Murder Frontend servers)
To use normal.conf, do:
cp master/conf/normal.conf /etc/cyrus.conf
Optionally, you can edit /etc/cyrus.conf to disable or enabling
certain services, or to tune the number of preforked copies. Be
sure not to remove the entries that are labeled required.
2. Arrange to start "/usr/cyrus/bin/master" as root when the system
starts. It will bind some ports and then give up it's root
privileges. Until your system reboots, you can start the master
process by hand:
/usr/cyrus/bin/master &
3. Monitor the progress of the master process by examining the
imapd.log file. It should never exit by itself, but you can shut
down the mail system by sending it a signal with kill.
Configuring the Mail Transfer Agent
In order to deliver mail to the Cyrus system, you'll have to configure
your MTA (Sendmail, Postfix, Exim, etc) to use LMTP.
Configuring Sendmail
Generate a sendmail configuration file which delivers local mail to the
IMAP server. See the file cf/README in the Sendmail distribution for
information on how to create a complete configuration file. This file
also lists variables that can be used to customize the mailer
definitions mentioned below.
The following configurations assume that you are using the lmtpunix
service from one of the sample cyrus.conf files discussed above.
* For Sendmail 8.12.4 and higher, use the cyrusv2 mailer definition
in the Sendmail distribution:
define(`confLOCAL_MAILER', `cyrusv2')
MAILER(`cyrusv2')
If you wish to change the name of the UNIX socket or switch to TCP,
define CYRUSV2_MAILER_ARGS appropriately as described in cf/README.
* For Sendmail 8.10 - 8.12.3, use the cyrusv2.mc file as a template
to create a Sendmail configuration file.
* For Sendmail 8.9.x and earlier, use the cyrus mailer definition in
the Sendmail distribution:
define(`confLOCAL_MAILER', `cyrus')
MAILER(`cyrus')
Edit /etc/group and add user "daemon" to the "mail" group. This
will permit sendmail to run the "deliver" (LMTP client) program to
deliver mail to the IMAP server.
Cyrus also includes a socket map daemon smmapd which can be used by
Sendmail 8.13 and higher (a patch for 8.12 is available) to verify at
RCPT TO time that a message can be delivered to the particular mailbox.
To use this daemon, add smmapd as a service in cyrus.conf and configure
Sendmail accordingly.
Configuring Postfix
The Postfix source distribution comes with the file
"README_FILES/LMTP_README". Even if you are using a binary distribution
of Postfix, it would be well worth your while to download the full
Postfix source. Not only will you get the above file, but numerous
other "readme" files and sample configuration files.
One thing you need to watch out for is the UID and GID of the Postfix
software. As it states in the Postfix "INSTALL" document, you must
create a new account that does not share its UID and GID with any other
user account. This is for security reasons. If you installed Postfix
with a GID of "mail", you will need to select a different GID for
Cyrus. See the Cyrus configure options "--with-cyrus-user" and
"--with-cyrus-group". (This was more crucial when the use of Cyrus'
"deliver" was more prevalent, but it is still a good idea to follow
this policy.)
Another thing to note is the location of your "sendmail" command. On
some platforms this will be "/usr/sbin/sendmail", on others,
"/usr/lib/sendmail". Cyrus will need to know where this command is. See
Installing Sieve for more details.
Assuming that you are using the lmtpunix service from one of the sample
cyrus.conf files discussed above, the Postfix configuration file
"/etc/postfix/main.cf" should have the following line:
mailbox_transport = lmtp:unix:/var/imap/socket/lmtp
Naturally, both the Postfix UID and the Cyrus UID need to be able to
access the specified socket file.
Starting with Postfix snapshot-20010222, you can improve the efficiency
of LMTP delivery via the "mailbox_transport" by putting the following
entries in "/etc/postfix/main.cf":
local_destination_recipient_limit = 300
local_destination_concurrency_limit = 5
Of course you should adjust these settings as appropriate for the
capacity of the hardware you are using. The recipient limit setting can
be used to take advantage of the single instance message store
capability of Cyrus. The concurrency limit can be used to control how
many simultaneous LMTP sessions will be permitted to the Cyrus message
store.
Additional examples are included in the Postfix file
"README_FILES/LMTP_README".
Configuring Exim 4
Generate an Exim configuration file which delivers local mail to the
IMAP server. See the Exim documentation for information on how to
create a complete configuration file.
Cyrus is designed to be used as a black-box server -- there are usually
no local user accounts. As a result, you must define the following
"router":
localuser:
driver = accept
transport = local_delivery
The following "transports" assume that you are using either the
lmtpunix or lmtp service from one of the sample cyrus.conf files
discussed above.
* Using lmtpunix (UNIX socket):
local_delivery:
driver = lmtp
command = "/usr/cyrus/bin/deliver -l"
batch_max = 20
user = cyrus
* Using lmtp (TCP socket -- Exim and Cyrus on same host):
local_delivery:
driver = smtp
protocol = lmtp
hosts = localhost
allow_localhost
For more advanced configurations (such as address verification, etc),
consult the Exim documentation and sample configurations.
Exporting Netnews via IMAP
If you wish to use export Netnews via IMAP, consult
install-netnews.html.
SSL, TLS, and OpenSSL
Transport Layer Security (TLS), is a standardized version of the Secure
Sockets Layer (SSL v3) standard. IMAP can make use of two different
versions of TLS/SSL: STARTTLS and an SSL wrapped session.
In STARTTLS, a client connects to the IMAP port as normal and then
issues the STARTTLS command, which begins a TLS negotiation. This is
currently supported by the Cyrus IMAP server when it is compiled with
OpenSSL.
The alternative, a SSL wrapped connection, involves the client
connected to a seperate port ("imaps") and negotiating a SSL session
before starting the IMAP protocol. Again, this is supported natively by
the Cyrus IMAP server when it is compiled with OpenSSL.
Both TLS and SSL require a server key and a certificate. Optionally, in
addition to establishing a secure connection, TLS can authenticate the
client.
Configuring Cyrus with OpenSSL
1.
OpenSSL requires the certificate and key in PEM format. You can
create the server's private key and certificate yourself using
OpenSSL. Here, we create a self-signed key for the machine "
foobar.andrew.cmu.edu" and put both the certificate and key in the
file "/var/imap/server.pem".
Please do not blindly enter in the information to OpenSSL below.
Instead, enter the appropriate information for your organization
(i.e. NOT Carnegie Mellon University for the Organization name,
etc.).
openssl req -new -x509 -nodes -out /var/imap/server.pem -keyout /var/imap/server.pem -days 365
Using configuration from /usr/local/lib/openssl/openssl.cnf
Generating a 1024 bit RSA private key
.............+++++
......................+++++
writing new private key to '/var/imap/server.pem'
-----
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [AU]:US
State or Province Name (full name) [Some-State]:Pennsylvania
Locality Name (eg, city) []:Pittsburgh
Organization Name (eg, company) [Internet Widgits Pty Ltd]:Carnegie Mellon University
Organizational Unit Name (eg, section) []:Andrew Systems Group
Common Name (eg, YOUR name) []:foobar.andrew.cmu.edu
Email Address []:
2. Make sure to make key file(s) readable by the Cyrus user. For
example: chown cyrus /var/imap/server.pem
3. Add the following to /etc/imapd.conf to tell the server where to
find the certificate and key file (used for ALL services):
tls_cert_file: /var/imap/server.pem
tls_key_file: /var/imap/server.pem
Optionally, you can use separate certificates and key files for
each service:
[servicename]_tls_cert_file: /var/imap/imap-server.pem
[servicename]_tls_key_file: /var/imap/imap-server.pem
"servicename" here refers to the name of the service as specified
in cyrus.conf. It is not necessaraly the name of the binary.
This is useful if you want to use different hostnames for each
service (e.g. via virtual host interfaces or DNS CNAMEs). In the
absence of any of the service specific options, the value of the
global option is used. A value of disabled for the certificate or
key file for a particular service will disable SSL/TLS for that
service.
If you have a Certificate Authority (CA), you may wish to generate
a certificate request and send it to be signed by your CA.
By default, Cyrus will cache SSL/TLS sessions for reuse for up to
24 hours. By adjusting the value of the tls_session_timeout option
in imapd.conf, the session caching can be disabled (0) or the
expiration period shortened.
4. You can test STARTTLS by using imtest:
imtest -t "" foobar.andrew.cmu.edu
Client-side certificates
Client certificates are somewhat harder to configure than server
certificates. You'll need a CA (certificate authority) and need to
generate client certificates signed by that CA. STARTTLS in Sendmail
and other MTAs have similiar problems, so Claus Assman's page is a good
reference.
You can use the self-signed certificate generated above as a CA for
client certificates. To do this, try the following:
TODO: write me!
Unfortunately, there's no standard on how to convert the client's
authenticate DN (distinguished name) to a SASL authentication name.
Alternate Namespace and UNIX Hierarchy Convention
If you wish to use the alternate namespace and/or the UNIX hierarchy
convention, consult altnamespace.html.