节选自《Netkiller Mail 手札》
6.1. Sender Policy Framework
6.1.1. 分析 SPF 记录
从主域开始查看 txt 记录
代码语言：javascript复制neo@netkiller:~$ nslookup -type=txt 163.com
Server: 8.8.8.8
Address: 8.8.8.8#53
Non-authoritative answer:
163.com text = "v=spf1 include:spf.163.com -all"
Authoritative answers can be found from: 找到 spf.163.com 域名，再查看它的 txt 记录
代码语言：javascript复制neo@netkiller:~$ nslookup -type=txt spf.163.com
Server: 8.8.8.8
Address: 8.8.8.8#53
Non-authoritative answer:
spf.163.com text = "v=spf1 include:a.spf.163.com include:b.spf.163.com include:c.spf.163.com include:d.spf.163.com -all"
Authoritative answers can be found from: 一次查看 a.spf.163.com ~ d.spf.163.com 几个域名
代码语言：javascript复制neo@netkiller:~$ nslookup -type=txt a.spf.163.com
Server: 8.8.8.8
Address: 8.8.8.8#53
Non-authoritative answer:
a.spf.163.com text = "v=spf1 ip4:220.181.12.0/22 ip4:220.181.31.0/24 ip4:123.125.50.0/24 ip4:220.181.72.0/24 ip4:123.58.178.0/24 ip4:123.58.177.0/24 ip4:113.108.225.0/24 ip4:218.107.63.0/24 ip4:123.58.189.128/25 -all"
Authoritative answers can be found from: 这样就可以获得163.com所有邮件服务器的IP地址
下面我们使用 dig 演示此过程
代码语言：javascript复制 neo@netkiller:~$ dig -t txt google.com
; <<>> DiG 9.9.5-11ubuntu1.2-Ubuntu <<>> -t txt google.com
;; global options: cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 55272
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;google.com. IN TXT
;; ANSWER SECTION:
google.com. 3599 IN TXT "v=spf1 include:_spf.google.com ~all"
;; Query time: 40 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Wed Feb 24 11:12:01 HKT 2016
;; MSG SIZE rcvd: 87
neo@netkiller:~$ dig -t txt _spf.google.com
; <<>> DiG 9.9.5-11ubuntu1.2-Ubuntu <<>> -t txt _spf.google.com
;; global options: cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 24347
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;_spf.google.com. IN TXT
;; ANSWER SECTION:
_spf.google.com. 299 IN TXT "v=spf1 include:_netblocks.google.com include:_netblocks2.google.com include:_netblocks3.google.com ~all"
;; Query time: 45 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Wed Feb 24 11:12:07 HKT 2016
;; MSG SIZE rcvd: 160
neo@netkiller:~$ dig -t txt _netblocks.google.com
; <<>> DiG 9.9.5-11ubuntu1.2-Ubuntu <<>> -t txt _netblocks.google.com
;; global options: cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 59355
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;_netblocks.google.com. IN TXT
;; ANSWER SECTION:
_netblocks.google.com. 3599 IN TXT "v=spf1 ip4:64.18.0.0/20 ip4:64.233.160.0/19 ip4:66.102.0.0/20 ip4:66.249.80.0/20 ip4:72.14.192.0/18 ip4:74.125.0.0/16 ip4:108.177.8.0/21 ip4:173.194.0.0/16 ip4:207.126.144.0/20 ip4:209.85.128.0/17 ip4:216.58.192.0/19 ip4:216.239.32.0/19 ~all"
;; Query time: 42 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Wed Feb 24 11:12:13 HKT 2016
;; MSG SIZE rcvd: 304 
