getmxrr()

(PHP 4, PHP 5, PHP 7)

获取互联网主机名对应的 MX 记录

说明

搜索$hostname对应的 MX DNS 记录。

参数

互联网主机名。

找到的 MX 记录列表存放于$mxhosts数组。

提供了$weight数组后，它会用找到的权重信息填充数组。

返回值

找到记录返回TRUE，没找到或者出错时返回FALSE。

更新日志

注释

本函数不应使用于地址验证。仅在 MX 记录在 DNS 中找到时才会返回，然而根据» RFC 2821，没有 MX 记录时，$hostname本身就是 MX 主机，优先级为0。Note:

在兼容 Windows 实现之前的版本，可以使用» PEARclass 的» Net_DNS。

参见

• checkdnsrr() 给指定的主机（域名）或者IP地址做DNS通信检查
• dns_get_record() 获取指定主机的DNS记录
• gethostbyname() 返回主机名对应的 IPv4地址。
• gethostbynamel() 获取互联网主机名对应的 IPv4 地址列表
• gethostbyaddr() 获取指定的IP地址对应的主机名
• Linux 手册页面named(8)

I tried using getmxrr() to validate the domain portion of email addresses in enquiry submission forms, and there is a curious effect with some top-level domains when checking non-existant domains.
With sdlkfjsdl.com, since the domain does not exist, getmxrr() returns false, as expected, and the returned mxhosts array is empty.
But with sdlkfjsdl.gov, getmxrr() returns true, and the returned mxhosts array contains one element: NULL
With sdlkfjsdl.org, getmxrr() returns true, and the returned mxhosts array contains one element: '0.0.0.0'
With sdlkfjsdl.co.uk, getmxrr() returns true and supplies one MX record: uk-net-wildcard-null-mx.centralnic.net
So to validate the email domain, it would seem one has to check the returned mxhosts array to exclude the possibility of mxhosts being returned as NULL, 0.0.0.0 and wildcard ...

An other way to do mx-lookup on a windows platform.
Rewrote this from an other class i wrote for DNS lookup - so it might be a bit messy - but hope you get the idea.
Big thanks to the rfc community.


Return:
02 MX Records Records returned for php.net:
Array
(
  [0] => Array
    (
      [MX_Pref] => 15
      [MX] => smtp.osuosl.org
    )
  [1] => Array
    (
      [MX_Pref] => 5
      [MX] => osu1.php.net
    )
)

I decided to have a bash at this after doing a bit of research... 

If greylisting is installed on the mx host then he send a "451 4.7.1 Please try again later"
My code fragment: 

Leonardt's code fails with multiple mx records with the same wight. You can easily change this by switching keys and values in the mxs array:
   for($i=0;$i

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