本篇記錄我修正 Linode 郵件伺服器沒有 PTR 記錄，被 Google 擋信問題的過程。
mail 指令發了一封測試信件：
date | mail -s test guozhao.wang@gmail.com
結果真的發不出去，在系統上收到 GMail 退回來的信件，完整的內容如下：
Date: Fri, 26 May 2017 11:32:33 +0800 From: Mail Delivery System <Mailer-Daemon@linode01.gtwang.org> To: seal@linode01.gtwang.org Subject: Mail delivery failed: returning message to sender This message was created automatically by mail delivery software. A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed: guozhao.wang@gmail.com SMTP error from remote mail server after end of data: host gmail-smtp-in.l.google.com [2404:6800:4003:c01::1b]: 550-5.7.1 [2400:8901::f03c:91ff:fe67:98b] Our system has detected that this 550-5.7.1 message does not meet IPv6 sending guidelines regarding PTR records 550-5.7.1 and authentication. Please review 550-5.7.1 https://support.google.com/mail/?p=IPv6AuthError for more information 550 5.7.1 . e6si11179112pgf.386 - gsmtp ------ This is a copy of the message, including all the headers. ------ Return-path: <seal@linode01.gtwang.org> Received: from seal by linode01.gtwang.org with local (Exim 4.82) (envelope-from <seal@linode01.gtwang.org>) id 1dE5zM-0006Xx-6E for guozhao.wang@gmail.com; Fri, 26 May 2017 11:32:32 +0800 Date: Fri, 26 May 2017 11:32:32 +0800 To: guozhao.wang@gmail.com Subject: test User-Agent: Heirloom mailx 12.5 6/20/10 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-Id: <E1dE5zM-0006Xx-6E@linode01.gtwang.org> From: Guo-Tzau Wang <seal@linode01.gtwang.org> Fri May 26 11:32:32 CST 2017
我用 dig 查了一下自己伺服器 IPv6 的反解（PTR）：
dig -x 2400:8901::f03c:91ff:fe67:98b
; <<>> DiG 9.9.5-3ubuntu0.14-Ubuntu <<>> -x 2400:8901::f03c:91ff:fe67:98b ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 56424 ;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 4096 ;; QUESTION SECTION: ;b.8.9.0.7.6.e.f.f.f.1.9.c.3.0.f.0.0.0.0.0.0.0.0.1.0.9.8.0.0.4.2.ip6.arpa. IN PTR ;; AUTHORITY SECTION: 1.0.9.8.0.0.4.2.ip6.arpa. 83890 IN SOA ns1.linode.com. dns.linode.com. 2017052592 14400 14400 1209600 86400 ;; Query time: 1 msec ;; SERVER: 139.162.21.5#53(139.162.21.5) ;; WHEN: Fri May 26 11:45:22 CST 2017 ;; MSG SIZE rcvd: 155
結果真的是我自己沒有設定。
由於這個反解要從主機商的 DNS 伺服器中修改，不同的虛擬主機商會有不同的作法，我的 WordPress 網站是使用 Linode VPS 架設的，所以要使用 Linode 所提供的 DNS 反解設定工具來設定。
修正完成並且等待 DNS 紀錄更新之後，再查詢一次反解紀錄：
dig -x 2400:8901::f03c:91ff:fe67:98b
; <<>> DiG 9.8.3-P1 <<>> -x 2400:8901::f03c:91ff:fe67:98b ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 40134 ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 5, ADDITIONAL: 10 ;; QUESTION SECTION: ;b.8.9.0.7.6.e.f.f.f.1.9.c.3.0.f.0.0.0.0.0.0.0.0.1.0.9.8.0.0.4.2.ip6.arpa. IN PTR ;; ANSWER SECTION: b.8.9.0.7.6.e.f.f.f.1.9.c.3.0.f.0.0.0.0.0.0.0.0.1.0.9.8.0.0.4.2.ip6.arpa. 86029 IN PTR linode01.gtwang.org. ;; AUTHORITY SECTION: 1.0.9.8.0.0.4.2.ip6.arpa. 86029 IN NS ns1.linode.com. 1.0.9.8.0.0.4.2.ip6.arpa. 86029 IN NS ns2.linode.com. 1.0.9.8.0.0.4.2.ip6.arpa. 86029 IN NS ns5.linode.com. 1.0.9.8.0.0.4.2.ip6.arpa. 86029 IN NS ns4.linode.com. 1.0.9.8.0.0.4.2.ip6.arpa. 86029 IN NS ns3.linode.com. ;; ADDITIONAL SECTION: ns1.linode.com. 97521 IN A 162.159.27.72 ns1.linode.com. 97521 IN AAAA 2400:cb00:2049:1::a29f:1a63 ns2.linode.com. 7910 IN A 162.159.24.39 ns2.linode.com. 7910 IN AAAA 2400:cb00:2049:1::a29f:1827 ns3.linode.com. 97521 IN A 162.159.25.129 ns3.linode.com. 97521 IN AAAA 2400:cb00:2049:1::a29f:1981 ns4.linode.com. 97521 IN A 162.159.26.99 ns4.linode.com. 97521 IN AAAA 2400:cb00:2049:1::a29f:1b48 ns5.linode.com. 97521 IN A 162.159.24.25 ns5.linode.com. 97521 IN AAAA 2400:cb00:2049:1::a29f:1819 ;; Query time: 4 msec ;; SERVER: 140.110.96.1#53(140.110.96.1) ;; WHEN: Fri May 26 12:13:45 2017 ;; MSG SIZE rcvd: 443
設定伺服器的 DNS 反解之後，就可以正常寄信了，不過後來因為網站留言的通知信太多了，又被 Google 當成垃圾信擋掉：
Date: Fri, 26 May 2017 12:54:32 +0800 From: Mail Delivery System <Mailer-Daemon@linode01.gtwang.org> To: www-data@linode01.gtwang.org Subject: Mail delivery failed: returning message to sender This message was created automatically by mail delivery software. A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed: guozhao.wang@gmail.com SMTP error from remote mail server after end of data: host gmail-smtp-in.l.google.com [2404:6800:4003:c03::1b]: 550-5.7.1 [2400:8901::f03c:91ff:fe67:98b 7] Our system has detected that 550-5.7.1 this message is likely unsolicited mail. To reduce the amount of spam 550-5.7.1 sent to Gmail, this message has been blocked. Please visit 550-5.7.1 https://support.google.com/mail/?p=UnsolicitedMessageError 550 5.7.1 for more information. s3si29651575plb.315 - gsmtp ------ This is a copy of the message, including all the headers. ------ Return-path: <www-data@linode01.gtwang.org> Received: from www-data by linode01.gtwang.org with local (Exim 4.82) (envelope-from <www-data@linode01.gtwang.org>) id 1dE7Gh-0006ot-MW for guozhao.wang@gmail.com; Fri, 26 May 2017 12:54:31 +0800 To: guozhao.wang@gmail.com Subject: =?UTF-8?B?77y7Ry4gVC4gV2FuZ++8veiri+WvqeaguO+8muOAjOS9v+eUqCBPcA==?= +=?UTF-8?B?ZW5TU0wg5oiWIEdudVBHIOWKoOWvhuaqlOahiOiIh+ebrumMhO+8jA==?= =?UTF-8?B?55So5a+G56K85LiK6Y6W5L+d6K235qmf5a+G6LOH5paZ44CN?= X-PHP-Originating-Script: 33:class-phpmailer.php Date: Fri, 26 May 2017 04:54:31 +0000 From: WordPress <wordpress@blog.gtwang.org> Message-ID: <bd6823e588c9792cc8d5f2cdcba457e1@blog.gtwang.org> X-Mailer: PHPMailer 5.2.22 (https://github.com/PHPMailer/PHPMailer) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit [略]
後來直接把迴響的 Email 通知功能關掉，這樣就不會產生太多類似的 Email，浪費系統資源。
www-data 信件由於長期被 Google 擋信，所有從 WordPress 發出又退回來的信件全部都送到系統的 www-data 帳號中，我檢查了一下 www-data 的信箱檔案，發現累積了不少信件：
ls -l /var/spool/mail/www-data
-rw-rw---- 1 www-data mail 57913373 May 26 12:26 /var/spool/mail/www-data
因為 www-data 是系統用的帳號，它的信平常不會有人去看，正常來說我們應該要把 www-data 的信件轉寄到系統管理者的帳號下（我之前忘記了），設定的方式是修改 /etc/aliases 設定檔，加入一行：
www-data: gtwang
這樣以後所有寄給 www-data 的信，就會自動轉寄給 gtwang 這個帳號了。
接著把 www-data 的舊信件刪掉：
sudo rm /var/spool/mail/www-data
參考資料：Google