为什么发送电子邮件需要多个邮件服务器跃点? [英] Why does sending an email need multiple mail server hops?

问题描述

当我向某人发送电子邮件时，(我认为)我的电子邮件已发送到我的家庭服务器，然后将该电子邮件发送到目标服务器，然后最终将其发送给我想发送给的人.

When I send an email to somebody, (I think) my email is sent to my home server, then the email is sent to target server, then it is finally sent to the people I want to send to.

有时候，这需要多次跳跃，这使我感到困惑.为什么这需要多跳?为什么不能将电子邮件直接发送到目标服务器?例如，XMPP不需要多跳.

Sometimes, this needs multiple hops, which is the point that confuses me. Why does this need multiple hops? Why can't the email be sent to the target server directly? XMPP doesn't need multiple hops, for example.

推荐答案

从根本上讲，这与Internet的原始目的有关，或更确切地说，它是Internet的前身

Fundamentally that has to do with the original purpose of the Internet, or rather it's predecessor ARPANET, was designed to survive the loss of portions of the network (popular to popular misconception, this design goal existed not in order to survive nuclear attack, but because network components were rather unreliable at the time).

数据包交换网络旨在查找一条或多条路由，从数据包开始(您的电子邮件客户端)到需要的路由(您要发送到的人的电子邮件客户端).

The packet switching network is designed to find one or more routes from where the packet starts (your email client) to where it needs to be (the email client of the person you are sending to).

为了获得这种灵活性，系统的设计不仅是直接从A点到B点进行路由，而且还从当前正在运行的可用路由(从可能的非常大的一组可能的路由中)中寻找可用的路由.

In order to achieve that flexibility, the system is designed not just to route directly from point A to point B, but to find an available route (from a possibly very large set of possible routes) that is currently functioning.

如果您的电子邮件客户端必须知道如何直接发送到世界上其他所有设备，而无需干预子网来管理流量，则您的计算机将需要直接连接到世界上其他所有计算机.那将是非常昂贵的.相反，它们之间的路由器会接受您和您所在区域其他人的数据包，并弄清楚如何将每个数据包路由到更接近其目的地的位置.这类似于航空公司用于设置区域航班的馈送枢纽的方法.

If your email client had to know how to directly send to every other device in the world, without intervening subnets managing traffic, your computer would need a direct connection to every other computer in the world. That would be prohibitively expensive. Instead, routers inbetween accept packets from you and other people in your area and figure out how to route each packet closer to its destination. That's similar to the method that the airlines use to have regional flights feed hubs.

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