电邮地址_电子邮件如何运作？

电邮地址

You send and receive it everyday, it’s instantaneous, and it doesn’t cost a thing. It’s email, one of the most important tools of today. Let’s take a look at how it works, under-the-hood and in normal language.

您每天都在发送和接收它，它是瞬时的，而且不需要花一分钱。这是电子邮件，是当今最重要的工具之一。让我们来看看它是如何工作的，它们是在引擎盖下和以正常语言显示的。

电子邮件到底是什么？ (What Exactly Is Email?)

Electronic mail (abbreviated as e-mail, email, E-Mail, etc.) is a very old form of computer-based communication. A long time ago – in technological, not human, terms – computers were giant machines. People used dial-up terminals to access them, and each machine held storage for multiple users. As is the case with any community, people found useful and unique ways to communicate with one another, and a messaging system evolved. The caveat was that you could only send messages to other users on the same system, at least up until 1971. As the story goes, along came Ray Tomlinson who sent the first email by addressing a user on another system using the ‘@’ symbol. Obviously, both the underlying dynamics and far-reaching consequences weren’t so simple, but it was that notion that brings us to where we are today.

电子邮件(缩写为电子邮件，电子邮件，电子邮件等)是一种非常古老的基于计算机的通信形式。很久以前-从技术而非人类的角度讲，计算机是巨型计算机。人们使用拨号终端访问它们，而每台计算机都为多个用户保留存储空间。与任何社区一样，人们发现了有用且独特的相互交流方式，并且消息传递系统得到了发展。需要注意的是，您只能向同一系统上的其他用户发送消息，至少直到1971年为止。故事的发展过程是雷·汤姆林森(Ray Tomlinson)，他通过使用'@'符号在另一个系统上向用户发送地址来发送第一封电子邮件。显然，潜在的动态变化和深远的影响并不是那么简单，但是正是这种观念将我们带到了今天。

(Image from ajmexico)

(图片来自ajmexico )

Email was, at that time, the equivalent of today’s text message. Over time, it changed and evolved like anything else; it has sender and receiver info, a subject line, a message body, and attachments, but on the whole, emails are pretty simple documents. It’s not so easy to get it from point A to point B, however. Like anything else, there’s an intricate process involved that works behind the scenes to make it seem as seamless as possible. A lot of the ideas used in relaying email were important in formulating document transfer, which is at the core of things like bulletin board systems and the world wide web.

电子邮件当时相当于今天的短信。随着时间的流逝，它像其他任何事物一样发生了变化和发展。它具有发送者和接收者的信息，主题行，消息正文和附件，但总的来说，电子邮件是非常简单的文档。但是，从A点到B点并不是那么容易。像其他任何事物一样，其中涉及一个复杂的过程，该过程在幕后起作用，以使其看起来尽可能无缝。中继电子邮件时使用的许多想法对于制定文档传输都很重要，而文档传输是公告板系统和万维网等内容的核心。

从发件人到收件人 (From Sender to Recipient)

Let’s start with an illustration of the process. It may not make complete sense at first, but it’ll be useful to refer back to.

让我们从过程的说明开始。乍一看可能没有完全意义，但回头参考会很有用。

When someone, let’s say a spice seller, sends an email, it has to have an address in the form of [email protected] Our example has [email protected] The email gets sent by the client to an outgoing mail server via Simple Mail Transfer Protocol. The SMTP server is like your local post office, which checks your postage and address and figures out where to send your mail. It doesn’t understand domains, though. They’re a sort of abstract thing, so the SMTP server contacts a Domain Name System server. The DNS server is a sort of phone or address book for the internet; it translates domains like “arrakis.com” to an IP address like “74.238.23.45.” Then, it finds out if that domain has any “MX” or mail exchange servers on it and makes a note of it. This is like your post office consulting maps of where your mail is supposed to go, calling their local post office, and checking to see if your friend has a mailbox or P.O. box to receive mail.

当某人(比如说香料销售商)发送电子邮件时，它必须具有[email protected]形式的地址。我们的示例是[email protected]。客户端通过简单邮件传输协议将电子邮件发送到外发邮件服务器。 SMTP服务器就像您当地的邮局一样，它检查您的邮资和地址并确定将邮件发送到哪里。但是，它不了解域。它们是一种抽象的事物，因此SMTP服务器与域名系统服务器联系。 DNS服务器是用于Internet的一种电话或地址簿。它将“ arrakis.com”之类的域名转换为“ 74.238.23.45”之类的IP地址。然后，它会发现该域上是否有任何“ MX”或邮件交换服务器，并记录下来。这就像您的邮局在咨询您的邮件去向的地图，致电其当地的邮局并检查您的朋友是否有邮箱或邮政信箱来接收邮件。

Now that the SMTP server has the proper info, the message gets sent from that server to the target domain’s mail exchange server. This server is referred to as an MTA, or Mail Transfer Agent. It decides where exactly to put the mail, much like how your friend’s post office figures out how best to get it delivered. Then, your friend goes and fetches the mail, usually using a client that works via POP or IMAP.

现在，SMTP服务器具有正确的信息，邮件将从该服务器发送到目标域的邮件交换服务器。该服务器称为MTA或邮件传输代理。它决定将邮件准确放置在何处，就像您朋友的邮局如何确定如何最好地发送邮件一样。然后，您的朋友通常使用通过POP或IMAP运行的客户端去获取邮件。

POP与IMAP (POP vs. IMAP)

These two acronyms plague email settings panels everywhere, so let’s take a deeper look at them. POP stands for Post Office Protocol. It’s useful because, like a post office, you can pop in, grab all of your mail, and then leave. You don’t need to stay connected, and aside from leaving a copy on the server, it’s a pretty cut-and-dry procedure. If you don’t leave a copy on the server, it doesn’t require much space or bandwidth either. You can use POP to grab mail from several different inboxes on several different email servers and consolidate them on one.

这两个首字母缩写困扰着电子邮件设置面板，因此让我们对其进行更深入的研究。 POP代表邮局协议。这很有用，因为您可以像邮局一样弹出，获取所有邮件，然后离开。您无需保持连接状态，除了在服务器上保留副本之外，这是一个非常简单的过程。如果您没有在服务器上保留副本，那么它也不需要太多空间或带宽。您可以使用POP从多个不同电子邮件服务器上的多个不同收件箱中提取邮件，并将它们合并到一个。

It has its drawbacks, though. POP is a unidirectional protocol; information travels one way. Once you download the email to a client, it’s up to the client to sort through its different statuses and so on. That’s fine if you only ever access mail from one place. Nowadays, though, it’s common to get email access from your phone’s client, the web interface when you’re away somewhere, and a client when you’re at home. It’d be tedious to sort through all of that info over several devices, assuming you’ve even kept a copy of each email on the server to begin with.

不过，它也有缺点。 POP是一种单向协议；信息传播是一种方式。将电子邮件下载到客户端后，由客户端决定其不同状态，依此类推。如果您只从一个地方访问邮件，那很好。但是，如今，从手机的客户端访问电子邮件，在外出时使用Web界面以及在家里时使用客户端都是很常见的。假设您甚至已经在服务器上保留了每封电子邮件的副本，那么在多个设备上对所有这些信息进行分类将很繁琐。

(Image from SuccessByDesigns)

(图片来自SuccessByDesigns )

IMAP’s a bit smarter about things. While POP can be considered to be very “client-oriented,” the Internet Message Access Protocol was designed to work in a different way: it’s “server-oriented,” and bi-directional. Clients have a two-way communication with their servers. All messages are kept on the server so multiple clients can access them. When you check an email on your phone, it’s marked as read and during the next interaction with the server, that status is sent back so all other clients can be updated with it. It’s like having your mail sent to an assistant at the post office who categorizes it and stores it for you, gives it to you whether you’re at home, at work, or actually there, and makes changes to the stored copies as you do.

IMAP在事情上比较聪明。尽管POP可以被认为是非常“面向客户端的”，但Internet消息访问协议却以不同的方式工作：“面向服务器”和双向。客户端与服务器之间进行双向通信。所有消息都保留在服务器上，以便多个客户端可以访问它们。当您在手机上检查电子邮件时，该电子邮件被标记为已读，并且在与服务器的下一次交互期间，该状态会被发送回，以便所有其他客户端都可以使用该电子邮件进行更新。就像将您的邮件发送给邮局的助理进行分类，然后将其存储为您，无论您是在家，在工作中还是在实际工作中，都可以将其发送给您，并在进行操作时对存储的副本进行更改。

You can keep a properly marked archive on your home client as well as on your mail server. IMAP also supports an offline mode; changes are synched with the server the next time you’re online. You can configure IMAP mail servers to fetch mail from POP inboxes, too, which works really well if you’re looking to consolidate. Of course, since IMAP works with the “cloud” ideal, server access and storage can be issues. Thankfully, storage space and bandwidth isn’t as expensive as it used to be, but this can definitely be a trade-off for some people.

您可以在家庭客户端以及邮件服务器上保留正确标记的存档。 IMAP还支持离线模式。下次您在线时，更改将与服务器同步。您也可以将IMAP邮件服务器配置为从POP收件箱中提取邮件，如果您希望进行合并，则效果很好。当然，由于IMAP可与“云”理想结合使用，因此服务器访问和存储可能会成为问题。值得庆幸的是，存储空间和带宽不像以前那样昂贵，但是对于某些人来说，这绝对是一个折衷。

SMTP和MTA (Both SMTP and MTA)

Unlike your physical mailbox, your outgoing and incoming mail are handled by two different types of servers. There’s really no discrimination towards receiving servers; any computer can be made an MTA pretty easily and handle things well. Sending mail is a different story. SMTP servers must have static IP addresses, and most ISPs block port 25 so that their users can’t send mail themselves. Why? Because of the massive amounts of spam gnawing away at our collective bandwidth, the very stuff your MTA should be configured to filter out. You can configure your clients to use your ISP’s SMTP server in lieu of running your own. The point is that you need both an MTA and an SMTP server to use email, as each is specialized for what it does.

与物理邮箱不同，传出和传入邮件由两种不同类型的服务器处理。接收服务器的确没有歧视。任何一台计算机都可以轻松地制成MTA，并且处理得很好。发送邮件是另一回事。 SMTP服务器必须具有静态IP地址，并且大多数ISP都阻止端口25，以便其用户无法自己发送邮件。为什么？由于大量垃圾邮件吞噬了我们的集体带宽，因此您的MTA应该配置为可以过滤掉的东西。您可以将客户端配置为使用ISP的SMTP服务器来代替运行自己的客户端。关键是，您既需要MTA也需要SMTP服务器来使用电子邮件，因为它们各自都专门用于处理电子邮件。

Email’s an important part of our everyday lives, but it’s nice to understand just how it works. After all, we wouldn’t have the internet without it.

电子邮件是我们日常生活的重要组成部分，但很高兴了解它的工作原理。毕竟，没有它，我们将没有互联网。

翻译自: https://www.howtogeek.com/56002/htg-explains-how-does-email-work/