1 - Purpose of this document ============================ This document describes how to build, install and configure a Postfix system so that it can do one of the following: - Send mail only, without changing an existing sendmail installation. - Send and receive mail via a virtual host interface, still without any change to an existing sendmail installation. - Replace sendmail altogether. 2 - Typographical conventions ============================= In the instructions below, a command written as # command should be executed as the superuser. A command written as % command should be executed as an unprivileged user. 3 - Documentation ================= Documentation is available as HTML web pages (point your browser to html/index.html) and as UNIX-style manpages (point your MANPATH environment variable to the `man' subdirectory; be sure to use an absolute path). The sample configuration files in the `conf' directory have extensive comments, but they may not describe every nuance of every feature. Many files have their own built-in manual page. Tools to extract those embedded manual pages are available in the mantools directory. 4 - Building on a supported system ================================== If your system is supported, it is one of AIX 3.2.5 AIX 4.1.x AIX 4.2.0 BSD/OS 2.x BSD/OS 3.x BSD/OS 4.x FreeBSD 2.x FreeBSD 3.x FreeBSD 4.x HP-UX 9.x HP-UX 10.x HP-UX 11.x IRIX 5.x IRIX 6.x Linux Debian 1.3.1 Linux Debian 2.x Linux RedHat 4.x Linux RedHat 5.x Linux RedHat 6.x Linux Slackware 3.5 Linux Slackware 4.0 Linux Slackware 7.0 Linux SuSE 5.x Linux SuSE 6.x Mac OS X server NEXTSTEP 3.x NetBSD 1.x OPENSTEP 4.x OSF1.V3 (Digital UNIX) OSF1.V4 aka Digital UNIX V4 OSF1.V5 aka Digital UNIX V5 OpenBSD 2.x Reliant UNIX 5.x Rhapsody 5.x SunOS 4.1.x SunOS 5.4..5.7 (Solaris 2.4..7) Ultrix 4.x or something closely resemblant. If at any time in the build process you get messages like: "make: don't know how to ..." you should be able to recover by running the following command from the Postfix top-level directory: % make -f Makefile.init makefiles If you copied the Postfix source code after building it on another machine, it is a good idea to cd into the top-level directory and % make tidy first. This will get rid of any system dependencies left over from compiling the software elsewhere. To build with GCC, or with the native compiler if people told me that is better for your system, just cd into the top-level Postfix directory of the source tree and type: % make To build with a non-default compiler, you need to specify the name of the compiler: % make makefiles CC=/opt/SUNWspro/bin/cc (Solaris) % make % make makefiles CC="/opt/ansic/bin/cc -Ae" (HP-UX) % make % make makefiles CC="purify cc" % make and so on. In some cases, optimization is turned off automatically. In order to build with non-default settings, for example, with a configuration directory other than /etc/postfix, use: % make makefiles CCARGS=-DDEF_CONFIG_DIR=\\\\\\\"/some/where\\\\\\\" % make That's seven backslashes :-) But at least this works with sh and csh. In any case, if the command % make produces compiler error messages, it may be time to examine the FAQ document. 5 - Porting to on an unsupported system ======================================= - Choose a SYSTEMTYPE name for the new system. Please use a name that includes the major version of the operating system (such as SUNOS4 or LINUX2), so that different releases of the same system can be supported without confusion. - Add a case statement to the "makedefs" shell script in the top-level directory that recognizes the new system reliably, and that emits the right system-specific information. Be sure to make the code robust against user PATH settings; if the system offers multiple UNIX flavors (e.g. BSD and SYSV) be sure to build for the native flavor, not the emulated one. - Add an #ifdef SYSTEMTYPE section to the central util/sys_defs.h include file. You may have to invent new feature macros. Please choose sensible feature macro names such as HAS_DBM or FIONREAD_IN_SYS_FILIO_H. I strongly recommend against #ifdef SYSTEMTYPE dependencies in individual source files. This may seem to be the quickest solution, but it will create a mess that becomes increasingly difficult to maintain over time. Moreover, with the next port you'd have to place #ifdefs all over the source code again. 6 - Installing the software after successful compilation ======================================================== IMPORTANT: if you are REPLACING an existing sendmail installation with Postfix, you may need to keep the old sendmail program running for some time in order to flush the mail queue. As superuser, execute the following commands (your sendmail, newaliases and mailq programs may be in a different place): # mv /usr/sbin/sendmail /usr/sbin/sendmail.OFF # mv /usr/bin/newaliases /usr/bin/newaliases.OFF # mv /usr/bin/mailq /usr/bin/mailq.OFF # chmod 755 /usr/sbin/sendmail.OFF /usr/bin/newaliases.OFF \ /usr/bin/mailq.OFF In order to install or upgrade Postfix: - Create a user "postfix" with a unique user id and group id. Preferably, this is an account that no-one can log into. The account does not need an executable login shell, and needs no existing home directory. My password file entry looks like this: postfix:*:12345:12345:postfix:/no/where:/no/shell - Make sure there is a corresponding alias in /etc/aliases: postfix: root - Review section 12 of this file, and decide if a world-writable maildrop is OK, or if Postfix needs a set-gid posting agent. - Run the INSTALL.sh script as the super-user: # sh INSTALL.sh The INSTALL.sh script offers suggestions for pathnames that you can override, either by editing INSTALL.sh or by specifying your preferences interactively. INSTALL.sh stores your preferences in the Postfix configuration directory in order to ease future installs. - Proceed to the section on how you wish to run Postfix on your particular machine: - Send mail only, without changing an existing sendmail installation (section 7). - Send and receive mail via a virtual host interface, still without any change to an existing sendmail installation (section 8). - Replace sendmail altogether (section 9). 7 - Configuring Postfix to send mail only ========================================= If you are going to use Postfix to send mail only, there is no need to change your existing sendmail setup. Instead, set up your mail user agent so that it calls the Postfix sendmail program directly. Follow the instructions in the "Mandatory configuration file edits" in section 10, review the "To chroot or not to chroot" text in section 11, and choose a security model according to section 12. You MUST comment out the `smtp inet' entry in /etc/postfix/master.cf, in order to avoid conflicts with the real sendmail. Start the Postfix system: # postfix start or, if you feel nostalgic, use the Postfix sendmail command: # sendmail -bd -qwhatever and watch your syslog file for any error messages. When it is run for the first time, the Postfix startup shell script will create a bunch of subdirectories below the Postfix spool directory. In order to inspect the mail queue, use % sendmail -bp See also the "Care and feeding" section 13 below. 8 - Configuring Postfix to send and receive mail (virtual interface) ==================================================================== Alternatively, you can use the Postfix system to send AND receive mail while leaving your sendmail setup intact, by running Postfix on a virtual interface address. Simply configure your mail user agent to directly invoke the Postfix sendmail program. The examples/virtual-setup directory gives instructions for setting up virtual interfaces for a variety of UNIX versions. In the /etc/postfix/main.cf file, I would specify myhostname = virtual.host.name inet_interfaces = $myhostname mydestination = $myhostname Follow the instructions in the "Mandatory configuration file edits" in section 10, review the "To chroot or not to chroot" text in section 11, and choose a security model according to section 12. Start the mail system: # postfix start or, if you feel nostalgic, use the Postfix sendmail program: # sendmail -bd -qwhatever and watch your syslog file for any error messages. When it is run for the first time, the Postfix startup shell script will create a bunch of subdirectories below the Postfix spool directory. In order to inspect the mail queue, use % sendmail -bp See also the "Care and feeding" section 13 below. 9 - Turning off sendmail forever ================================ Prior to installing Postfix you should save the existing sendmail program files as described in section 6. Be sure to keep the old sendmail running for at least a couple days to flush any unsent mail. To do so, stop the sendmail daemon and restart it as: # /usr/sbin/sendmail.OFF -q After you have visited the "Mandatory configuration file edits" section below, you can start the Postfix system with # postfix start But the good old sendmail way works just as well: # sendmail -bd -qwhatever and watch the syslog file for any complaints from the mail system. When it is run for the first time, the Postfix startup shell script will create a bunch of subdirectories below the Postfix spool directory. See also the "Care and feeding" section 13 below. 10 - Mandatory configuration file edits ======================================= By default, Postfix configuration files are in /etc/postfix, and must be owned by root. Giving someone else write permission to main.cf or master.cf means giving root privileges to that person. Whenever you make a change to a config file, execute the following command in order to refresh a running mail system: # postfix reload In /etc/postfix/main.cf you will have to set up a minimal number of configuration parameters. Postfix configuration parameters resemble shell variables. You specify a variable as parameter = value and you use it by putting a $ in front of its name: other_parameter = $parameter You can use $parameter before it is given a value. The Postfix configuration language uses lazy evaluation, and does not look at a parameter value until it is needed at runtime. First of all, you must specify what domain will be appended to a local address. The "myorigin" parameter defaults to the local hostname, but that is probably OK only for very small sites. Some examples: myorigin = $myhostname myorigin = $mydomain In the first case, local mail goes out as user@$myhostname, in the second case the sender address is user@$mydomain. Next you need to specify what mail addresses are local to the Postfix system. Some examples: mydestination = $myhostname, localhost.$mydomain mydestination = $myhostname, localhost.$mydomain, $mydomain mydestination = $myhostname The first example is appropriate for a workstation, the second is appropriate for the mailserver for an entire domain. The third example should be used when running on a virtual host interface. If you're behind a firewall, you should set up a relayhost. If you can, specify the organizational domain name so that Postfix can use DNS lookups, and so that it can fall back to a secondary MX host when the primary MX host is down. Otherwise just specify a hard-coded hostname. Some examples: relayhost = $mydomain relayhost = mail.$mydomain relayhost = [mail.$mydomain] The form enclosed with [] eliminates DNS MX lookups. By default, the SMTP client will do DNS lookups for sender and recipient addresses even when you specify a relay host. If your machine has no access to a DNS server, turn off SMTP client DNS lookups like this: disable_dns_lookups = yes The FAQ (html/faq.html) has more hints and tips for firewalled and/or dial-up networks. Finally, if you haven't used Sendmail prior to using Postfix, you will have to build the alias database (with: sendmail -bi, or: newaliases). Be sure to set up aliases for root and postmaster that forward mail to a real person. 11 - To chroot or not to chroot ============================== Most Postfix daemons can run in a chroot jail, that is, in a chroot environment at fixed low privilege. This provides a significant barrier against intrusion. The barrier is not impenetrable, but every little bit helps. The file /etc/postfix/master.cf by default runs no Postfix daemons in a chroot jail. However, with the exception of the `local' and `pipe' daemons, every Postfix daemon can run chrooted. The examples/chroot-setup directory has a collection of scripts for setting up chroot environments for Postfix systems. 12 - Security: writable versus protected maildrop directory =========================================================== Postfix offers a choice of submission mechanims. 1 - Postfix can use a world-writable, sticky, mode 1733 maildrop directory where local users can submit mail. This approach avoids the need for set-uid or set-gid software. Mail can be posted even while the mail system is down. Queue files in the maildrop directory have no read/write/execute permission for other users. The maildrop directory is not used for mail received via the network. With directory world write permission come opportunities for annoyance: a local user can make hard links to someone else's maildrop files so they don't go away and may be delivered multiple times; a local user can fill the maildrop directory with junk and try to crash the mail system; and a local user can hard link someone else's files into the maildrop directory and try to have them delivered as mail. However, Postfix queue files have a specific format; less than one in 10^12 non-Postfix files would be recognized as a valid Postfix queue file. In order to enable maildrop world-write permission: - Specify "no" when asked by the INSTALL.sh script whether Postfix needs set-gid privileges. 2 - On systems with many users it may be desirable to revoke maildrop directory world write permission, and to enable set-gid privileges on a small "maildrop" command that is provided for this purpose. In order to revoke maildrop world-write permission: - Create a group "maildrop" that is unique and that does not share its group ID with any other user, certainly not with the postfix account, - Specify "maildrop" when asked by the INSTALL.sh script whether Postfix needs set-gid privileges. The sendmail posting program will automatically invoke the postdrop command when maildrop directory write permission is restricted. 13 - Care and feeding of the Postfix system =========================================== The Postfix programs log all problems to the syslog daemon. The names of logfiles are specified in /etc/syslog.conf. Note: the syslogd will not create files. You must create them ahead of time before (re)starting syslogd. At the very least you need something like: mail.err /dev/console mail.debug /var/log/maillog Hopefully, the number of problems will be small, but it is a good idea to run every night before the syslog files are rotated: # postfix check # egrep '(reject|warning|error|fatal|panic):' /some/log/file The second line looks for problem reports from the mail software, and reports how effective the anti-relay and anti-UCE blocks are.