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  1. Agustin's Linux Manual
  2. Networks & Servers
  3. About the Author
  4. Table of Contents
  5. IP Addresses Networks and Subnets
  6. Network Classes
  7. IP Address in Decimal Notation
  8. Sub-netting
  9. Designing Subnets
  10. Allocating Subnets
  11. Defining Host Addresses
  12. Variable Length Subnet Mask
  13. Routing Protocols
  14. Classless Internet Domain Routing
  15. Servers - Chapter 9
  16. Apache Web Server
  17. Configuring Apache
  18. Uploading Web Pages
  19. Apache Overview
  20. MIMEMagic
  21. DNS Servers
  22. Welcome to Webmin
  23. Creating the Master Domain
  24. Adding the Reverse Zone
  25. Querying the DNS server
  26. Adding Virtual Domain to DNS Server
  27. Reverse Zone for Virtual Zone
  28. Binding IP Address for Virtual Domain
  29. Virtual Web Hosting
  30. DNS Security Options
  31. FTP Server
  32. Securing the FTP Server
  33. Email Server
  34. Postfix Configuration
  35. Dealing with Identical Users
  36. Configuring Email Clients
  37. Configuring Outlook
  38. Samba Server
  39. Configuring SAMBA Server
  40. The smb.conf File
  41. smb.conf Analysis
  42. Adding Users to Samba

Email Server

Postfix Email Server

What did I tell you? Didn't I tell you that you got the whole package for free? And yes, but Postfix is not the only email server available for Linux. If I am not mistaken Sendmail is the first email server that was available for Linux, but because of its complex configuration and security concerns, many email servers were started to merge in this open source movement, including qmail, Postfix and others.

Because of being “security conscious” in Postfix, it has earned its respect among Linux professionals and became an alternative to Sendmail. I myself have turned Postfix into my favorite email server.

During your Linux installation, you probably already installed Postfix. But in case you didn't, please refer to software installation earlier in this book. Because postfix runs in conjunction with a POP3 Server you need to install the IMAP package, POP3 is encapsulated within the IMAP package and when installed runs on demand.

The Postfix service is probably already running. Most of the servers run automatically after installation. If the server is not running and you need it to run automatically at startup, you have to configure it in linuxconf, if it is not listed under services, that means that it is not installed.

To start the service under the console:

[root@server2 root]# service postfix start

To restart the service under the console:

[root@server2 root]# service postfix restart

To stop the service:

[root@server2 root]# service postfix stop

I assume that you got it running in one way or another; so I will continue with the configuration. Configuring Postfix is quite simple, and I am sure that you will have it configured in no time.

The primary configuration file is /etc/postfix/main.cf. Depending on the distribution, this file may be located in a different directory. However, no matter where it is located, it is the same principle in the configuration.

[root@server2 postfix]# vi main.cf
# Global Postfix configuration file. This file #lists only a subset
# of all 100+ parameters. See the sample-xxx.cf #files for a full list.
# 
# The general format is lines with parameter = #value pairs. Lines
# that begin with whitespace continue the #previous line. A value can
# contain references to other $names or #${name}s.
#
# NOTE - CHANGE NO MORE THAN 2-3 PARAMETERS AT A TIME, AND TEST IF
# POSTFIX STILL WORKS AFTER EVERY CHANGE.

# SOFT BOUNCE
#
# The soft_bounce parameter provides a limited #safety net for
# testing.  When soft_bounce is enabled, mail #will remain queued that
# would otherwise bounce. This parameter #disables locally-generated
# bounces, and prevents the SMTP server from #rejecting mail permanently
# (by changing 5xx replies into 4xx replies). #However, soft_bounce
# is no cure for address rewriting mistakes or #mail routing mistakes.
#
#soft_bounce = no

# LOCAL PATHNAME INFORMATION
#
# The queue_directory specifies the location of #the Postfix queue.
# This is also the root directory of Postfix #daemons that run chrooted.
# See the files in examples/chroot-setup for #setting up Postfix chroot
# environments on different UNIX systems.
#
queue_directory = /var/spool/postfix

# The command_directory parameter specifies the #location of all
# postXXX commands.  The default value is #$program_directory.
#
command_directory = /usr/sbin

# The daemon_directory parameter specifies the #location of all Postfix
# daemon programs (i.e. programs listed in the master.cf file). The
# default value is $program_directory. This #directory must be owned
# by root.
#
daemon_directory = /usr/lib/postfix

# QUEUE AND PROCESS OWNERSHIP
#
# The mail_owner parameter specifies the owner #of the Postfix queue
# and of most Postfix daemon processes.  #Specify the name of a user
# account THAT DOES NOT SHARE ITS USER OR GROUP #ID WITH OTHER ACCOUNTS
# AND THAT OWNS NO OTHER FILES OR PROCESSES ON #THE SYSTEM.  In
# particular, don't specify nobody or daemon. #PLEASE USE A DEDICATED
# USER.
#

#mail_owner = postfix

# The default_privs parameter specifies the #default rights used by
# the local delivery agent for delivery to #external file or command.
# These rights are used in the absence of a #recipient user context.
# DO NOT SPECIFY A PRIVILEGED USER OR THE #POSTFIX OWNER.
#
#default_privs = nobody


# INTERNET HOST AND DOMAIN NAMES
# 
# The myhostname parameter specifies the #internet hostname of this
# mail system. The default is to use the fully-#qualified domain name
# from gethostname(). $myhostname is used as a #default value for many
# other configuration parameters.
#
#myhostname = host.domain.tld
#myhostname = virtual.domain.tld

# The mydomain parameter specifies the local #internet domain name.
# The default is to use $myhostname minus the #first component.
# $mydomain is used as a default value for many #other configuration
# parameters.
#
#mydomain = domain.tld

# SENDING MAIL
# 
# The myorigin parameter specifies the domain #that locally-posted
# mail appears to come from. The default is to #append $myhostname,
# which is fine for small sites.  If you run a #domain with multiple
# machines, you should (1) change this to #$mydomain and (2) set up
# a domain-wide alias database that aliases #each user to
# user@that.users.mailhost.
#
#myorigin = $myhostname

myorigin = $mydomain

# RECEIVING MAIL

# The inet_interfaces parameter specifies the #network interface
# addresses that this mail system receives mail #on.  By default,
# the software claims all active interfaces on #the machine. The
# parameter also controls delivery of mail to #user@[ip.address].
#
#inet_interfaces = localhost
#inet_interfaces = all
#inet_interfaces = $myhostname
#inet_interfaces = $myhostname, localhost

# The mydestination parameter specifies the #list of domains that this
# machine considers itself the final #destination for. That includes
# Sendmail-style virtual domains hosted on this #machine.
#
# Do not include Postfix-style virtual domains #- those domains are
# specified elsewhere (see sample-virtual.cf, #and sample-transport.cf).
#
# The default is $myhostname + #localhost.$mydomain.  On a mail domain
# gateway, you should also include $mydomain. #Do not specify the
# names of domains that this machine is backup #MX host for. Specify
# those names via the relay_domains or #permit_mx_backup settings for
# the SMTP server (see sample-smtpd.cf).
#
# The local machine is always the final #destination for mail addressed
# to user@[the.net.work.address] of an #interface that the mail system
# receives mail on (see the inet_interfaces #parameter).
#
# Specify a list of host or domain names, #/file/name or type:table
# patterns, separated by commas and/or #whitespace. A /file/name
# pattern is replaced by its contents; a #type:table is matched when
# a name matches a lookup key.  Continue long #lines by starting the
# next line with whitespace.
#

mydestination = $myhostname, localhost.$mydomain, /etc/postfix/mydestination

#mydestination = $myhostname, localhost.$mydomain $mydomain
#mydestination = $myhostname, localhost.$mydomain, $mydomain,
#	mail.$mydomain, www.$mydomain, ftp.$mydomain


# TRUST AND RELAY CONTROL

# The mynetworks parameter specifies the list #of "trusted" SMTP
# clients that have more privileges than #"strangers".
#
# In particular, "trusted" SMTP clients are #allowed to relay mail
# through Postfix.  See the #smtpd_recipient_restrictions parameter
# in file sample-smtpd.cf.
#
# You can specify the list of "trusted" network #addresses by hand
# or you can let Postfix do it for you (which #is the default).
#
# By default (mynetworks_style = subnet), #Postfix "trusts" SMTP
# clients in the same IP subnetworks as the #local machine.
# On Linux, this does works correctly only with #interfaces specified
# with the "ifconfig" command.
# 
# Specify "mynetworks_style = class" when #Postfix should "trust" SMTP
# clients in the same IP class A/B/C networks #as the local machine.
# Don't do this with a dialup site - it would #cause Postfix to "trust"
# your entire provider's network.  Instead, #specify an explicit
# mynetworks list by hand, as described below.
#  
# Specify "mynetworks_style = host" when #Postfix should "trust"
# only the local machine.
# 
#mynetworks_style = class
#mynetworks_style = subnet
#mynetworks_style = host

# Alternatively, you can specify the mynetworks #list by hand, in
# which case Postfix ignores the #mynetworks_style setting.
#
# Specify an explicit list of network/netmask #patterns, where the
# mask specifies the number of bits in the #network part of a host
# address.
#
# You can also specify the absolute pathname of #a pattern file instead
# of listing the patterns here. Specify #type:table for table-based #lookups
# (the value on the table right-hand side is #not used).
#
#mynetworks = 168.100.189.0/28, 127.0.0.0/8
#mynetworks = $config_directory/mynetworks
#mynetworks = hash:/etc/postfix/network_table

# The relay_domains parameter restricts what #clients this mail system
# will relay mail from, or what destinations #this system will relay
# mail to.  See the #smtpd_recipient_restrictions restriction in #the
# file sample-smtpd.cf for detailed #information.
#
# By default, Postfix relays mail
# - from "trusted" clients whose IP address #matches $mynetworks, 
# - from "trusted" clients matching #$relay_domains or subdomains #thereof,
# - from untrusted clients to destinations that #match $relay_domains
#   or subdomains thereof, except addresses #with sender-specified #routing.
# The default relay_domains value is #$mydestination.
# 
# In addition to the above, the Postfix SMTP #server by default accepts #mail
# that Postfix is final destination for:
# - destinations that match $inet_interfaces,
# - destinations that match $mydestination
# - destinations that match $virtual_maps.
# These destinations do not need to be listed #in $relay_domains.
# 
# Specify a list of hosts or domains, #/file/name patterns or type:name
# lookup tables, separated by commas and/or #whitespace.  Continue
# long lines by starting the next line with whitespace. A file name
# is replaced by its contents; a type:name #table is matched when a
# (parent) domain appears as lookup key.
#
# NOTE: Postfix will not automatically forward #mail for domains that
# list this system as their primary or backup #MX host. See the
# permit_mx_backup restriction in the file #sample-smtpd.cf.
#
#relay_domains = $mydestination


# INTERNET OR INTRANET

# The relayhost parameter specifies the default #host to send mail to
# when no entry is matched in the optional #transport(5) table. When
# no relayhost is given, mail is routed #directly to the destination.
#
# On an intranet, specify the organizational #domain name. If your
# internal DNS uses no MX records, specify the #name of the intranet
# gateway host instead.
#
# In the case of SMTP, specify a domain, host, #host:port, [host]:port,
# [address] or [address]:port; the form [host] #turns off MX lookups.
#
# If you're connected via UUCP, see also the #default_transport #parameter.
#
#relayhost = $mydomain
#relayhost = gateway.my.domain
#relayhost = uucphost
#relayhost = [an.ip.add.ress]

# REJECTING UNKNOWN LOCAL USERS
#
# The local_recipient_maps parameter specifies #optional lookup tables
# with all names (not addresses) of users that #are local with respect
# to $mydestination and $inet_interfaces.  If #this parameter is
# defined, then the SMTP server will reject #mail for unknown local
# users.
#
# If you use the default Postfix local delivery #agent for local
# delivery, uncomment the definition below.
#
# Beware: if the Postfix SMTP server runs #chrooted, you may have to
# copy the passwd (not shadow) database into the jail. This is
# system dependent.
# 
#local_recipient_maps = $alias_maps unix:passwd.byname

# INPUT RATE CONTROL
#
# The in_flow_delay configuration parameter #implements mail input
# flow control. This feature is turned on by #default, although it
# still needs further development (it's #disabled on SCO UNIX due
# to an SCO bug).
# 
# A Postfix process will pause for $in_flow_delay seconds before
# accepting a new message, when the message #arrival rate exceeds the
# message delivery rate. With the default 50 #SMTP server process
# limit, this limits the mail inflow to 50 #messages a second more
# than the number of messages delivered per #second.
# 
# Specify 0 to disable the feature. Valid #delays are 0..10.
# 
#in_flow_delay = 1s

# ADDRESS REWRITING
#
# Insert text from sample-rewrite.cf if you #need to do address
# masquerading.
#
# Insert text from sample-canonical.cf if you #need to do address
# rewriting, or if you need username->Firstname.Lastname mapping.

# ADDRESS REDIRECTION (VIRTUAL DOMAIN)
#
# Insert text from sample-virtual.cf if you #need virtual domain #support.



# "USER HAS MOVED" BOUNCE MESSAGES
#
# Insert text from sample-relocated.cf if you #need "user has moved"
# style bounce messages. Alternatively, you can #bounce recipients
# with an SMTP server access table. See sample-#smtpd.cf.

# TRANSPORT MAP
#
# Insert text from sample-transport.cf if you #need explicit routing.

# ALIAS DATABASE
#
# The alias_maps parameter specifies the list #of alias databases used
# by the local delivery agent. The default list #is system dependent.
# On systems with NIS, the default is to search #the local alias
# database, then the NIS alias database. See #aliases(5) for syntax
# details.
# 
# If you change the alias database, run #"postalias /etc/aliases" (or
# wherever your system stores the mail alias #file), or simply run
# "newaliases" to build the necessary DBM or DB #file.
#
# It will take a minute or so before changes #become visible.  Use
# "postfix reload" to eliminate the delay.
#
#alias_maps = dbm:/etc/aliases

alias_maps = hash:/etc/postfix/aliases

#alias_maps = hash:/etc/aliases, #nis:mail.aliases
#alias_maps = netinfo:/aliases

# The alias_database parameter specifies the #alias database(s) that
# are built with "newaliases" or "sendmail -#bi".  This is a separate
# configuration parameter, because alias_maps #(see above) may specify
# tables that are not necessarily all under #control by Postfix.
#
#alias_database = dbm:/etc/aliases
#alias_database = dbm:/etc/mail/aliases
#alias_database = hash:/etc/aliases
#alias_database = hash:/etc/aliases, hash:/opt/majordomo/aliases

# ADDRESS EXTENSIONS (e.g., user+foo)
#
# The recipient_delimiter parameter specifies #the separator between
# user names and address extensions (user+foo). #See canonical(5),
# local(8), relocated(5) and virtual(5) for the #effects this has on
# aliases, canonical, virtual, relocated and .forward file lookups.
# Basically, the software tries user+foo and .forward+foo before
# trying user and .forward.
#

#recipient_delimiter = +

# DELIVERY TO MAILBOX
#
# The home_mailbox parameter specifies the #optional pathname of a
# mailbox file relative to a user's home #directory. The default
# mailbox file is /var/spool/mail/user or #/var/mail/user.  Specify
# "Maildir/" for qmail-style delivery (the / is #required).
#
#home_mailbox = Mailbox
#home_mailbox = Maildir/
 
# The mail_spool_directory parameter specifies the directory where
# UNIX-style mailboxes are kept. The default setting depends on the
# system type.
#
#mail_spool_directory = /var/mail

mail_spool_directory = /var/spool/mail

# The mailbox_command parameter specifies the optional external
# command to use instead of mailbox delivery. The command is run as
# the recipient with proper HOME, SHELL and LOGNAME environment #settings.
# Exception:  delivery for root is done as $default_user.
#
# Other environment variables of interest: USER (recipient username),
# EXTENSION (address extension), DOMAIN (domain part of address),
# and LOCAL (the address localpart).
#
# Unlike other Postfix configuration parameters, the mailbox_command
# parameter is not subjected to $parameter substitutions. This is to
# make it easier to specify shell syntax (see example below).
#
# Avoid shell meta characters because they will force Postfix to run
# an expensive shell process. Procmail alone is expensive enough.
#
# IF YOU USE THIS TO DELIVER MAIL SYSTEM-WIDE, YOU MUST SET UP AN
# ALIAS THAT FORWARDS MAIL FOR ROOT TO A REAL USER.
#
#mailbox_command = /some/where/procmail
#mailbox_command = /some/where/procmail -a "$EXTENSION"

mailbox_command = /usr/bin/procmail -Y -a $DOMAIN

# The mailbox_transport specifies the optional transport in master.cf
# to use after processing aliases and .forward files. This parameter
# has precedence over the mailbox_command, fallback_transport and
# luser_relay parameters.
#
# Specify a string of the form transport:nexthop, where transport is
# the name of a mail delivery transport defined in master.cf.  The
# :nexthop part is optional. For more details see the sample transport
# configuration file.
#
#mailbox_transport = lmtp:unix:/file/name
#mailbox_transport = cyrus

# The fallback_transport specifies the optional transport in master.cf
# to use for recipients that are not found in the UNIX passwd database.
# This parameter has precedence over the luser_relay parameter.
#
# Specify a string of the form transport:nexthop, where transport is
# the name of a mail delivery transport defined in master.cf.  The
# :nexthop part is optional. For more details see the sample transport
# configuration file.
#
#fallback_transport = lmtp:unix:/file/name
#fallback_transport = cyrus
#fallback_transport =

# The luser_relay parameter specifies an optional destination address
# for unknown recipients.  By default, mail for unknown local #recipients
# is bounced.
#
# The following expansions are done on luser_relay: $user (recipient
# username), $shell (recipient shell), $home (recipient home #directory),
# $recipient (full recipient address), $extension (recipient address
# extension), $domain (recipient domain), $local (entire recipient
# localpart), $recipient_delimiter. Specify ${name?value} or
# ${name:value} to expand value only when $name does (does not) exist.
#
# luser_relay works only for the default Postfix local delivery agent.
#
#luser_relay = $user@other.host
#luser_relay = $local@other.host
#luser_relay = admin+$local
  
# JUNK MAIL CONTROLS
# 
# The controls listed here are only a very small subset. See the file
# sample-smtpd.cf for an elaborate list of anti-UCE controls.

# The header_checks parameter specifies an optional table with patterns
# that each logical message header is matched against, including
# headers that span multiple physical lines.  Patterns are matched
# in the specified order, and the search stops upon the first match.
# When a pattern matches, what happens next depends on the associated
# action that is specified in the right-hand side of the table:
#
# REJECT the entire message is rejected.
# REJECT text.... The text is sent to the originator.
# IGNORE the header line is silently discarded.
# WARN   the header is logged (not rejected) with a warning message.
# WARN text... as above, and the text is logged, too.
#
# These patterns do not apply to MIME headers in the message body.
#
# See also the body_checks example in the sample-filter.cf file.
#

#header_checks = regexp:/etc/postfix/header_checks

# FAST ETRN SERVICE
#
# Postfix maintains per-destination logfiles with information about
# deferred mail, so that mail can be flushed quickly with the SMTP
# "ETRN domain.tld" command, or by executing "sendmail -qRdomain.tld".
# 
# By default, Postfix maintains deferred mail logfile information
# only for destinations that Postfix is willing to relay to (as
# specified in the relay_domains parameter). For other destinations,
# Postfix attempts to deliver ALL queued mail after receiving the
# SMTP "ETRN domain.tld" command, or after execution of "sendmail
# -qRdomain.tld". This can be slow when a lot of mail is queued.
# 
# The fast_flush_domains parameter controls what destinations are
# eligible for this "fast ETRN/sendmail -qR" service.
# 
#fast_flush_domains = $relay_domains
#fast_flush_domains =

# SHOW SOFTWARE VERSION OR NOT
#
# The smtpd_banner parameter specifies the text that follows the 220
# code in the SMTP server's greeting banner. Some people like to see
# the mail version advertised. By default, Postfix shows no version.
#
# You MUST specify $myhostname at the start of the text. That is an
# RFC requirement. Postfix itself does not care.
#
#smtpd_banner = $myhostname ESMTP $mail_name
#smtpd_banner = $myhostname ESMTP $mail_name ($mail_version)
smtpd_banner = $myhostname ESMTP $mail_name ($mail_version) (Mandrake Linux)

# PARALLEL DELIVERY TO THE SAME DESTINATION
#
# How many parallel deliveries to the same user or domain? With local
# delivery, it does not make sense to do massively parallel delivery
# to the same user, because mailbox updates must happen sequentially,
# and expensive pipelines in .forward files can cause disasters when
# too many are run at the same time. With SMTP deliveries, 10
# simultaneous connections to the same domain could be sufficient to
# raise eyebrows.
# 
# Each message delivery transport has its #XXX_destination_concurrency_limit
# parameter.  The default is $default_destination_concurrency_limit for
# most delivery transports. For the local delivery agent the default is #2.

#local_destination_concurrency_limit = 2
#default_destination_concurrency_limit = 10

# DEBUGGING CONTROL
#
# The debug_peer_level parameter specifies the increment in verbose
# logging level when an SMTP client or server host name or address
# matches a pattern in the debug_peer_list parameter.
#
debug_peer_level = 2

# The debug_peer_list parameter specifies an optional list of domain
# or network patterns, /file/name patterns or type:name tables. When
# an SMTP client or server host name or address matches a pattern,
# increase the verbose logging level by the amount specified in the
# debug_peer_level parameter.
#
#debug_peer_list = 127.0.0.1
#debug_peer_list = some.domain

# The debugger_command specifies the external command that is executed
# when a Postfix daemon program is run with the -D option.
#
# Use "command .. & sleep 5" so that the debugger can attach before
# the process marches on. If you use an X-based debugger, be sure to
# set up your XAUTHORITY environment variable before starting Postfix.
#
debugger_command =
	 PATH=/usr/bin:/usr/X11R6/bin
	 xxgdb $daemon_directory/$process_name $process_id & sleep 5

# OTHER OPTIONS (Mandrake)
# The delay_warning_time specifies after how many hours a warning
# is sent that mail has not yet been delivered. By default, no warning
# is sent.
#

delay_warning_time = 4

# INSTALL-TIME CONFIGURATION INFORMATION
#
# The following parameters are used when installing a new Postfix #version.
# 
# sendmail_path: The full pathname of the Postfix sendmail command.
# This is the Sendmail-compatible mail posting interface.
# 

sendmail_path = /usr/sbin/sendmail.postfix

# newaliases_path: The full pathname of the Postfix newaliases command.
# This is the Sendmail-compatible command to build alias databases.
#
newaliases_path = /usr/bin/newaliases.postfix

# mailq_path: The full pathname of the Postfix mailq command.  This
# is the Sendmail-compatible mail queue listing command.
# 

mailq_path = /usr/bin/mailq.postfix

# setgid_group: The group for mail submission and queue management
# commands.  This must be a group name with a numerical group ID that
# is not shared with other accounts, not even with the Postfix account.
#

setgid_group = postdrop

# manpage_directory: The location of the Postfix on-line manual pages.
#
manpage_directory = /usr/share/man

# sample_directory: The location of the Postfix sample configuration #files.
#
sample_directory = /usr/share/doc/postfix-1.1.11/samples

# readme_directory: The location of the Postfix README files.
#
readme_directory = /usr/share/doc/postfix-1.1.11/README_FILES
alias_database = hash:/etc/postfix/aliases