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DNS使用MX記錄來(lái)實(shí)現(xiàn)郵件路由,它規(guī)定了域名的郵件服務(wù)器要么處理,要么向前轉(zhuǎn)發(fā)有關(guān)該域名的郵件.處理郵件是指將其傳送給其地址所關(guān)聯(lián)的個(gè)人,向前轉(zhuǎn)發(fā)郵件是指通過(guò)SMTP協(xié)議將其傳送給其最終目的地.為了防止郵遞路由,MX記錄除了郵件交換器的域名外還有一個(gè)特殊參數(shù):優(yōu)先級(jí)值.優(yōu)先級(jí)值是個(gè)從0 到65535的無(wú)符號(hào)整數(shù),它給出郵件交換器的優(yōu)先級(jí)別.

    優(yōu)先級(jí)值自身并不重要,關(guān)鍵在于它同其它郵件交換器的優(yōu)先級(jí)值的相對(duì)大小,優(yōu)先級(jí)值相對(duì)越小,優(yōu)先級(jí)越高.郵件總是首先試圖傳遞給優(yōu)先級(jí)值相對(duì)最小的郵件交換器.失敗后才試圖傳遞給優(yōu)先級(jí)值稍大的郵件交換器.郵件總是試遍了同一優(yōu)先級(jí)的郵件交換器,失敗后才試圖傳遞給優(yōu)先級(jí)稍低的郵件交換器.

注意你列為郵件交換器的主機(jī)必須擁有地址記錄.

 

下面列出幾個(gè)我用nslookup程序查詢(xún)的記錄：
lee@work:~$ nslookup
> set type=mx
> hnby.com.cn
Server:         10.10.16.60
Address:        10.10.16.60#53

Non-authoritative answer:
*** Can't find hnby.com.cn: No answer    //沒(méi)有郵件交換

Authoritative answers can be found from:
hnby.com.cn
        origin = dns.hnby.com.cn
        mail addr = root.hnby.com.cn
        serial = 2002120101
        refresh = 900
        retry = 600
        expire = 86400
        minimum = 3600
> set type=mx
> henan.gov.cn
Server:         10.10.16.60
Address:        10.10.16.60#53

Non-authoritative answer:
*** Can't find henan.gov.cn: No answer

Authoritative answers can be found from:
henan.gov.cn
        origin = ns.hazzptt.net.cn
        mail addr = root.ns.hazzptt.net.cn
        serial = 99968011
        refresh = 28899
        retry = 7200
        expire = 604800
        minimum = 86400
> set type=mx
> yahoo.com.cn
Server:         10.10.16.60
Address:        10.10.16.60#53

Non-authoritative answer:
yahoo.com.cn    mail exchanger = 10 mta-v1.mail.vip.cnb.yahoo.com. ／／雅虎中國(guó)的郵件交換服務(wù)

Authoritative answers can be found from:
yahoo.com.cn    nameserver = ns8.yahoo.com.
yahoo.com.cn    nameserver = ns9.yahoo.com.
yahoo.com.cn    nameserver = ns1.yahoo.com.
yahoo.com.cn    nameserver = ns3.yahoo.com.
yahoo.com.cn    nameserver = ns6.yahoo.com.
ns1.yahoo.com   internet address = 66.218.71.63
ns3.yahoo.com   internet address = 217.12.4.104
ns6.yahoo.com   internet address = 202.43.223.170
> set type=mx
> yahoo.com
Server:         10.10.16.60
Address:        10.10.16.60#53

Non-authoritative answer:
yahoo.com       mail exchanger = 1 mx3.mail.yahoo.com.
yahoo.com       mail exchanger = 1 mx1.mail.yahoo.com.
yahoo.com       mail exchanger = 1 mx2.mail.yahoo.com.

Authoritative answers can be found from:
yahoo.com       nameserver = ns1.yahoo.com.
yahoo.com       nameserver = ns2.yahoo.com.
yahoo.com       nameserver = ns3.yahoo.com.
yahoo.com       nameserver = ns4.yahoo.com.
yahoo.com       nameserver = ns5.yahoo.com.
mx3.mail.yahoo.com      internet address = 4.79.181.12
mx3.mail.yahoo.com      internet address = 67.28.113.10
mx3.mail.yahoo.com      internet address = 4.79.181.168
mx3.mail.yahoo.com      internet address = 4.79.181.134
mx3.mail.yahoo.com      internet address = 67.28.113.74
mx1.mail.yahoo.com      internet address = 67.28.113.71
mx1.mail.yahoo.com      internet address = 67.28.113.73
mx1.mail.yahoo.com      internet address = 67.28.113.19
mx1.mail.yahoo.com      internet address = 4.79.181.14
mx1.mail.yahoo.com      internet address = 4.79.181.15
mx1.mail.yahoo.com      internet address = 4.79.181.168
mx2.mail.yahoo.com      internet address = 4.79.181.135
mx2.mail.yahoo.com      internet address = 4.79.181.136
mx2.mail.yahoo.com      internet address = 4.79.181.168
mx2.mail.yahoo.com      internet address = 67.28.113.70
mx2.mail.yahoo.com      internet address = 67.28.113.72
ns1.yahoo.com   internet address = 66.218.71.63
ns2.yahoo.com   internet address = 66.163.169.170
ns3.yahoo.com   internet address = 217.12.4.104
ns4.yahoo.com   internet address = 68.142.196.63
> set type=mx
> dahew.com.cn
Server:         10.10.16.60
Address:        10.10.16.60#53

*** Can't find dahew.com.cn: No answer
> set type=mx
> dahew.com
Server:         10.10.16.60
Address:        10.10.16.60#53

Non-authoritative answer:
dahew.com       mail exchanger = 10 mail1.dahew.com.

Authoritative answers can be found from:
dahew.com       nameserver = ns1.dns-diy.com.
dahew.com       nameserver = ns2.dns-diy.com.
mail1.dahew.com internet address = 219.156.123.177
ns1.dns-diy.com internet address = 210.51.187.81
ns1.dns-diy.com internet address = 218.16.225.50
ns1.dns-diy.com internet address = 60.191.252.66
ns2.dns-diy.com internet address = 218.107.207.123
ns2.dns-diy.com internet address = 218.85.134.143
ns2.dns-diy.com internet address = 64.84.29.59


當(dāng)我們?cè)赽ind中配置的時(shí)候，作如下語(yǔ)句：
$TTL 3h

@ SOA my.test.com.  root.test.com. (
;                                ^^^^  
;                              
　　　　　　　　2000020501;序列號(hào)
3h;　3小時(shí)后刷新
1h;  1小時(shí)后彼一時(shí)試
1w;  1周后期滿(mǎn)
1h)  否定緩存TTL為1小時(shí)


他們有區(qū)別吧，@　在SOA類(lèi)型記錄的名字字段中指的是當(dāng)前的源，是test.com

NS　IN ns.test.com.
;    名字服務(wù)器
MX　IN 10  mx.myhome.com.
;   郵件服務(wù)器
ns.myhome.com.  IN A 192.168.1.1
mx.myhome.com.   IN A 192.168.1.1

事情總是在看到過(guò)之后才能真正的了解?？茖W(xué)的理性精神，但是實(shí)際的操作是需要實(shí)證主義的！