发出给企业的邮件总是被退信

企业邮箱可能设置了，拒收垃圾邮件的功能；

你的163邮箱如果是免费的那种，可能企业VIP邮箱会不认同吧~~

还有就是：附件太大，传图或文件内容太多，影响发信速度导致失败；

或者地址错误，邮箱停用，邮箱之间不兼容……

当您telnet AOL MX记录的时候，会出现下面这些类似的信息：

220-rly-ya06.mx.aol.com ESMTP mail_relay_in-ya6.3Fri, 20 Jan 2006 22:15:42 -05 00

220-America Online (AOL) and its affiliated companies do not

220- authorize the use of its proprietary computers and computer

220- networks to accept, transmit, or distribute unsolicited bulk

220- e-mail sent from the internet. Effective immediately: AOL

220- may no longer accept connections from IP addresses which

220 have no reverse-DNS (PTR record) assigned.

Reverse Lookup causes additional overhead on servers, but is commonly used to help prevent environments from getting unsolicited e-mail messages (spam). You can configure your SMTP server to perform reverse lookups on incoming e-mail messages. This makes sure that the IP address and the fully qualified domain name (FQDN) of the sender's e-mail message server match the sender's domain name.

The mail servers of some Internet domains require that you create a valid PTR record that points the sending server's IP address to the local SMTP domain namespace. Sometimes these mail servers require that the PTR record match the actual FQDN of their SMTP Virtual Server on Exchange. Typically, this is the MX record. These Internet domains include AOL.com, Qwest.net, Mindspring, Earthlink, and Hotmail. To send mail to these domains, create a valid PTR or a reverse lookup record on your company’s external or Internet DNS server.

我简单翻译一下上面这段话的含义：

反向解析会增加服务器的负载，但是通常可以用它来阻止接收垃圾邮件。您能够设置您的SMTP服务器对入站邮件执行反向解析。这可以确保发件人邮件服务器的IP和FQDN与发件人的域名相匹配。

有些一些Internet 域的邮件服务器要求您创建一个有效的PTR记录来将发送服务器的IP指向本地SMTP域名称空间。有些时候这些邮件服务器要求PTR记录和Exchange 上它们的SMTP虚拟服务器的实际FQDN相匹配。通常情况下，这就是MX记录。这些Internet 域包含AOL.com, Qwest.net, Mindspring, Earthlink, and Hotmail。

要发送邮件给这些域，必须在您的公司的外部或者Internet DNS服务器上创建有效的PTR或反向解析记录。

例如，您的Exchange Server位于防火墙后面，它的内部IP地址是10.10.10.1。防火墙的外部IP地址是4.3.2.1。

当Exchange Server通过防火墙发送邮件给destination.com域，接收邮件服务器看到SMTP连接的地址是4.3.2.1。接收电子邮件服务器根据这个地址执行反向DNS查询，而不一定是MX记录。接收方服务器找到的4.3.2.1PTR记录必须指向source.com域的有效的主机记录。

详细的信息，请参考下面的文章：

You are unable to send or receive SMTP messages from certain Internet domains in Exchange 2000 Server, in Exchange Server 2003, and in Small Business Server 2003

http://support.microsoft.com/kb/300171/en-us

这是我转的一篇，关于你的问题在微软的论坛上有，你也可以上去看下，那边还是比较专业的，希望可以帮到你

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