为什么电子邮件客户端需要SMTP中继服务器?那有必要吗? [英] Why email client need a SMTP relay server? Is that neccessary?

问题描述

设置我的移动电子邮件客户端时，通常需要输入SMTP中继服务器域名，但是为什么我的电子邮件客户端完全需要SMTP中继服务器?

When setting-up my mobile email client, I usually need to enter the SMTP relay server domain name, but why my email client need a SMTP relay server at all?

我认为通过查找DNS MX记录，它可以直接与目标电子邮件地址来自哪个域的smtpd服务器(例如postfix)进行通信.并直接发送给它，为什么不呢?

I think it can directly talk to the smtpd server (e.g. postfix) from which domain the destination Email address is, by looking up the DNS MX records. And send directly to it, why not?

实际上，我还有另一个困惑，如果smtpd服务器使用SMTP AUTH，那么其他地方的依赖服务器如何才能依靠邮件呢?依赖服务器根本没有传输该邮件所需的用户名和密码.

Actually I have another confusion, if a smtpd server use SMTP AUTH, then how can a rely server elsewhere rely a mail to it? The rely server simply don't have the username and password necessary to transfer that mail.

推荐答案

电子邮件客户端使用SMTP中继服务器进行

Email clients use SMTP relay server to

• 简化电子邮件发送(例如，避免重复通过电子邮件客户端进行传递尝试)
• 避免被误认为是垃圾邮件发送者.

在古老的垃圾邮件以前，直接发送电子邮件可能是一个相当简单的选择.

Direct email sending might be a reasonably simple option in ancient pre spam past.

SMTP AUTH(主要)与电子邮件客户端一起用于电子邮件服务器通信.在不禁止来自陌生人"的电子邮件的情况下，SMTP服务器到SMTP服务器的通信不需要SMTP AUTH.SMTP AUTH允许接受来自受信任的客户端(客户)的邮件，甚至接受来自IP地址的邮件，否则这些邮件将被 DNSBL (例如 DUL 范围).

SMTP AUTH is used (mainly) with email client to email server communication. SMTP server to SMTP server communication could not require SMTP AUTH without prohibiting email from "strangers". SMTP AUTH allows to accept messages from trusted clients (customers) even from IP addresses that otherwise would be blocked by DNSBL (e.g. DUL ranges).

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