邮件技术

e-mail 系统共有三个主要的组成功能。首先是 Mail User Agent (MUA)，这是用户发送和读取邮件的程序。然后是 Mail Transfer Agent (MTA)，用来将邮件从一台计算机传递到另一台。最后是 Mail Delivery Agent (MDA)，用于将收到的邮件投递到用户的收件箱。

这三项功能可以由不同的程序执行，但也能合并到一个或两个程序里。还可以用不同的程序处理不同类型的邮件。

什么是FQDN
FQDN全名Fully Qualified Domain Name,一个域的全名。
命名规则：只能使用字符：a---z、A---Z、0---9和减号

 

What is a FQDN?

A FQDN is a Fully Qualified Domain Name.

A FQDN is a complete DNS name. For example, if a server named snoopy existed at the White House, the FQDN of that server might be snoopy.whitehouse.gov.

Technically, a FQDN must end in a period. This rule is almost always ignored.

A FQDN is limited to a maximum length of 255 characters.

In addition, the FQDN is also limited by the rules which limit each of its component sections. Each section must be made up only of letters, numbers, and the hyphen character. The characters are not case-sensitive. Each section of an FQDN can be up to 63 characters long.

什么是MX记录？

用于电子邮件系统发邮件时根据受信人的地址后缀来定位邮件服务器。例如，当收件人为“[e-mail]”时， 系统将对“mydomain.com”进行DNS中的MX记录解析。如果MX记录存在，系统就根据MX记录的优先级， 将邮件转发到与该MX相应的邮件服务器上。