[CentOS] Postfix (MTA: Mail transfer agent) インストール

1. yum を使ってパッケージをインストールする

   # yum -y install postfix

2. postfix の設定 (/etc/postfix/main.cf)
   • サーバーのホスト名を追加

     # 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
     myhostname = testserver.local ★

   • ドメイン名を追加

     # 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
     mydomain = local ★

   • ローカルからメールを送る時に送信元メールアドレスの @ 以降に追加するドメイン名を指定

     # 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

   • メールボックス形式を Maildir にする

     # 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 = Mail/ ★

   • 外部からのメール受信を許可する

     # 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 = all
     #inet_interfaces = $myhostname
     #inet_interfaces = $myhostname, localhost
     #inet_interfaces = localhost
     inet_interfaces = all ★

   • 自ドメイン宛メールを受信できるようにする

     # 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

3. sendmail を停止する

   # /etc/rc.d/init.d/sendmail stop
   sm-client を停止中:                                        [  OK  ]
   sendmail を停止中:                                         [  OK  ]
   # chkconfig sendmail off
   # chkconfig --list sendmail
   sendmail        0:off   1:off   2:off   3:off   4:off   5:off   6:off

4. システムで使用するメールサーバー機能を sendmail から Postfix に切り替える

   # alternatives --config mta
   
   2 プログラムがあり 'mta' を提供します。
   
     選択       コマンド
   -----------------------------------------------
   *+ 1           /usr/sbin/sendmail.sendmail
      2           /usr/sbin/sendmail.postfix
   
   Enter を押して現在の選択 [+] を保持するか、選択番号を入力します:2

5. Postfix 起動

   # /etc/rc.d/init.d/postfix start
   postfix を起動中:                                          [  OK  ]

6. Postfix を自動起動するように設定する

   # chkconfig postfix on
   # chkconfig --list postfix
   postfix         0:off   1:off   2:on    3:on    4:on    5:on    6:off