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.