Postfix can be used internally as a central SMTP server to decrease the complexity of future changes in configuration.

vim /etc/postfix/main.cf
 Global Postfix configuration file. This file lists only a subset
  of all parameters. For the syntax, and for a complete parameter
  list, see the postconf(5) manual page (command: "man 5 postconf").
  #
  For common configuration examples, see BASIC_CONFIGURATION_README
  and STANDARD_CONFIGURATION_README. To find these documents, use
  the command "postconf html_directory readme_directory", or go to
  http://www.postfix.org/.
  #
  For best results, 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.
  #
  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). This
  directory must be owned by root.
  #
  daemon_directory = /usr/libexec/postfix
  The data_directory parameter specifies the location of Postfix-writable
  data files (caches, random numbers). This directory must be owned
  by the mail_owner account (see below).
  #
  data_directory = /var/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 = smtp.provlima.com
  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 = provlima.com
  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.
  #
  For the sake of consistency between sender and recipient addresses,
  myorigin also specifies the default domain name that is appended
  to recipient addresses that have no @domain part.
  #
  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].
  #
  See also the proxy_interfaces parameter, for network addresses that
  are forwarded to us via a proxy or network address translator.
  #
  Note: you need to stop/start Postfix when this parameter changes.
  #
  inet_interfaces = 10.4.1.10
  inet_interfaces = $myhostname
  inet_interfaces = $myhostname, localhost
  inet_interfaces = localhost
  Enable IPv4, and IPv6 if supported
  inet_protocols = ipv4
  The proxy_interfaces parameter specifies the network interface
  addresses that this mail system receives mail on by way of a
  proxy or network address translation unit. This setting extends
  the address list specified with the inet_interfaces parameter.
  #
  You must specify your proxy/NAT addresses when your system is a
  backup MX host for other domains, otherwise mail delivery loops
  will happen when the primary MX host is down.
  #
  proxy_interfaces =
  proxy_interfaces = 1.2.3.4
  The mydestination parameter specifies the list of domains that this
  machine considers itself the final destination for.
  #
  These domains are routed to the delivery agent specified with the
  local_transport parameter setting. By default, that is the UNIX
  compatible delivery agent that lookups all recipients in /etc/passwd
  and /etc/aliases or their equivalent.
  #
  The default is $myhostname + localhost.$mydomain.  On a mail domain
  gateway, you should also include $mydomain.
  #
  Do not specify the names of virtual domains - those domains are
  specified elsewhere (see VIRTUAL_README).
  #
  Do not specify the names of domains that this machine is backup MX
  host for. Specify those names via the relay_domains settings for
  the SMTP server, or use permit_mx_backup if you are lazy (see
  STANDARD_CONFIGURATION_README).
  #
  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 (the right-hand side is ignored).
  Continue long lines by starting the next line with whitespace.
  #
  See also below, section "REJECTING MAIL FOR UNKNOWN LOCAL USERS".
  #
  mydestination = $myhostname, localhost.$mydomain, localhost
  mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain
  mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain,
  mail.$mydomain, www.$mydomain, ftp.$mydomain
  REJECTING MAIL FOR UNKNOWN LOCAL USERS
  #
  The local_recipient_maps parameter specifies optional lookup tables
  with all names or addresses of users that are local with respect
  to $mydestination, $inet_interfaces or $proxy_interfaces.
  #
  If this parameter is defined, then the SMTP server will reject
  mail for unknown local users. This parameter is defined by default.
  #
  To turn off local recipient checking in the SMTP server, specify
  local_recipient_maps = (i.e. empty).
  #
  The default setting assumes that you use the default Postfix local
  delivery agent for local delivery. You need to update the
  local_recipient_maps setting if:
  #
 You define $mydestination domain recipients in files other than
 /etc/passwd, /etc/aliases, or the $virtual_alias_maps files.
 For example, you define $mydestination domain recipients in
 the $virtual_mailbox_maps files.
 #
 You redefine the local delivery agent in master.cf.
 #
 You redefine the "local_transport" setting in main.cf.
 #
 You use the "luser_relay", "mailbox_transport", or "fallback_transport"
 feature of the Postfix local delivery agent (see local(8)).
 #
 Details are described in the LOCAL_RECIPIENT_README file.
 #
 Beware: if the Postfix SMTP server runs chrooted, you probably have
 to access the passwd file via the proxymap service, in order to
 overcome chroot restrictions. The alternative, having a copy of
 the system passwd file in the chroot jail is just not practical.
 #
 The right-hand side of the lookup tables is conveniently ignored.
 In the left-hand side, specify a bare username, an @domain.tld
 wild-card, or specify a user@domain.tld address.
 #
 local_recipient_maps = unix:passwd.byname $alias_maps
 local_recipient_maps = proxy:unix:passwd.byname $alias_maps
 local_recipient_maps =
 The unknown_local_recipient_reject_code specifies the SMTP server
 response code when a recipient domain matches $mydestination or
 ${proxy,inet}_interfaces, while $local_recipient_maps is non-empty
 and the recipient address or address local-part is not found.
 #
 The default setting is 550 (reject mail) but it is safer to start
 with 450 (try again later) until you are certain that your
 local_recipient_maps settings are OK.
 #
 unknown_local_recipient_reject_code = 550
 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 postconf(5).
 #
 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 = 192.168.1.0/24 10.5.1.0/22 172.16.70.0/16
 mynetworks = $config_directory/mynetworks
 mynetworks = hash:/etc/postfix/network_table
 The relay_domains parameter restricts what destinations this system will
 relay mail to.  See the smtpd_recipient_restrictions description in
 postconf(5) for detailed information.
 #
 By default, Postfix relays mail
 from "trusted" clients (IP address matches $mynetworks) to any destination,
 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 or $proxy_interfaces,
 destinations that match $mydestination
 destinations that match $virtual_alias_domains,
 destinations that match $virtual_mailbox_domains.
 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 description in postconf(5).
 #
 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 = [gateway.my.domain]
 relayhost = [mailserver.isp.tld]
 relayhost = uucphost
 relayhost = [an.ip.add.ress]
 REJECTING UNKNOWN RELAY USERS
 #
 The relay_recipient_maps parameter specifies optional lookup tables
 with all addresses in the domains that match $relay_domains.
 #
 If this parameter is defined, then the SMTP server will reject
 mail for unknown relay users. This feature is off by default.
 #
 The right-hand side of the lookup tables is conveniently ignored.
 In the left-hand side, specify an @domain.tld wild-card, or specify
 a user@domain.tld address.
 #
 relay_recipient_maps = hash:/etc/postfix/relay_recipients
 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 100 SMTP server process
 limit, this limits the mail inflow to 100 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
 #
 The ADDRESS_REWRITING_README document gives information about
 address masquerading or other forms of address rewriting including
 username->Firstname.Lastname mapping.
 ADDRESS REDIRECTION (VIRTUAL DOMAIN)
 #
 The VIRTUAL_README document gives information about the many forms
 of domain hosting that Postfix supports.
 "USER HAS MOVED" BOUNCE MESSAGES
 #
 See the discussion in the ADDRESS_REWRITING_README document.
 TRANSPORT MAP
 #
 See the discussion in the ADDRESS_REWRITING_README document.
 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/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"
 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.
 #
 NOTE: if you use this feature for accounts not in the UNIX password
 file, then you must update the "local_recipient_maps" setting in
 the main.cf file, otherwise the SMTP server will reject mail for
 non-UNIX accounts with "User unknown in local recipient table".
 #
 Cyrus IMAP over LMTP. Specify ``lmtpunix      cmd="lmtpd"
 listen="/var/imap/socket/lmtp" prefork=0'' in cyrus.conf.
 mailbox_transport = lmtp:unix:/var/lib/imap/socket/lmtp
 If using the cyrus-imapd IMAP server deliver local mail to the IMAP
 server using LMTP (Local Mail Transport Protocol), this is prefered
 over the older cyrus deliver program by setting the
 mailbox_transport as below:
 #
 mailbox_transport = lmtp:unix:/var/lib/imap/socket/lmtp
 #
 The efficiency of LMTP delivery for cyrus-imapd can be enhanced via
 these settings.
 #
 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.
 #
 Cyrus IMAP via command line. Uncomment the "cyrus…pipe" and
 subsequent line in master.cf.
 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.
 #
 NOTE: if you use this feature for accounts not in the UNIX password
 file, then you must update the "local_recipient_maps" setting in
 the main.cf file, otherwise the SMTP server will reject mail for
 non-UNIX accounts with "User unknown in local recipient table".
 #
 fallback_transport = lmtp:unix:/var/lib/imap/socket/lmtp
 fallback_transport =
 The luser_relay parameter specifies an optional destination address
 for unknown recipients.  By default, mail for unknown@$mydestination,
 unknown@[$inet_interfaces] or unknown@[$proxy_interfaces] is returned
 as undeliverable.
 #
 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.
 #
 NOTE: if you use this feature for accounts not in the UNIX password
 file, then you must specify "local_recipient_maps =" (i.e. empty) in
 the main.cf file, otherwise the SMTP server will reject mail for
 non-UNIX accounts with "User unknown in local recipient table".
 #
 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. The file
 SMTPD_ACCESS_README provides an overview.
 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.
 #
 By default, these patterns also apply to MIME headers and to the
 headers of attached messages. With older Postfix versions, MIME and
 attached message headers were treated as body text.
 #
 For details, see "man header_checks".
 #
 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".
 See the ETRN_README document for a detailed description.
 #
 The fast_flush_domains parameter controls what destinations are
 eligible for this service. By default, they are all domains that
 this server is willing to relay mail to.
 #
 fast_flush_domains = $relay_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)
 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 = 20
 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=/bin:/usr/bin:/usr/local/bin:/usr/X11R6/bin
       ddd $daemon_directory/$process_name $process_id & sleep 5
 If you can't use X, use this to capture the call stack when a
 daemon crashes. The result is in a file in the configuration
 directory, and is named after the process name and the process ID.
 #
 debugger_command =
 PATH=/bin:/usr/bin:/usr/local/bin; export PATH; (echo cont;
 echo where) | gdb $daemon_directory/$process_name $process_id 2>&1 
   $config_directory/$process_name.$process_id.log & sleep 5
    #
    Another possibility is to run gdb under a detached screen session.
    To attach to the screen sesssion, su root and run "screen -r
    " where  uniquely matches one of the detached
    sessions (from "screen -list").
    #
    debugger_command =
    PATH=/bin:/usr/bin:/sbin:/usr/sbin; export PATH; screen
    -dmS $process_name gdb $daemon_directory/$process_name
    $process_id & sleep 1
    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
    html_directory: The location of the Postfix HTML documentation.
    #
    html_directory = no
    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.
    This parameter is obsolete as of Postfix 2.1.
    #
    sample_directory = /usr/share/doc/postfix-2.10.1/samples
    readme_directory: The location of the Postfix README files.
    #
    readme_directory = /usr/share/doc/postfix-2.10.1/README_FILES
    relayhost = [email-smtp.us-west-2.amazonaws.com]:587
    smtp_tls_note_starttls_offer = yes
    smtp_tls_security_level = encrypt
    smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
    smtp_sasl_security_options = noanonymous
    smtp_sasl_auth_enable = yes
    smtp_use_tls = yes
    smtp_tls_CAfile = /etc/ssl/certs/ca-bundle.crt