服务器在电子邮件的图像请求中收到什么？ [英] What's does a server receive in an image request from email?
问题描述
采取这种情况：
- 我发送一个包含嵌入其中的图像的HTML电子邮件 - 例如使用标签
- 我打开电子邮件
- 请求图片
在图像请求期间，发送到服务器的完整信息是什么？有人可以粘贴它吗？
During that image request, what is the full set of information sent to the server? Can someone paste it in?
希望看到完整的请求&在Outlook等客户端打开电子邮件以及至少一个像Gmail这样的Gmail邮件平台的邮件头。
Would love to see the full request & header when the email is opened in a client like Outlook and at least one webmail platform like Gmail.
关于哪个服务器 - 我猜HTTP？如果我在Gmail中查看电子邮件，并且通过HTTP提供标签，那么是吗？
As to the comment about which server -- I guess HTTP? If I'm viewing an email in Gmail, and an tag is served, that is being served over HTTP, right?
谢谢！
推荐答案
就客户端计算机而言，邮件客户端应用程序与基于Web的邮件前端完全不同。
As far as the client computer is concerned, mail client applications are completely different from a web-based mail front-end.
通常，邮件客户端应用程序（正式邮件用户代理或MUA ）使用邮件专用协议，例如 POP3 或 IMAP 访问远程服务器上的邮箱。
Typically, mail client applications (formally Mail User Agents or MUAs) use a mail-specific protocol such as POP3 or IMAP to access a mailbox on a remote server.
根据协议，MUA可能必须在显示任何东西（POP3）之前下载整个消息，或者它可以请求每个 MIME 附件（IMAP）。通常，图像作为MIME附件被包含，并以可打印的形式（即限于 7位ASCII ）使用像 Base64 这样的东西，以确保递送而不会损坏。
Depending on the capabilities of the protocol, the MUA may have to download a whole message before displaying anything (POP3) or it may be able to request each MIME attachment separately (IMAP). Usually images are included as MIME attachments and are encoded in a printable form (i.e. restricted to 7-bit ASCII) using something like Base64, in order to ensure delivery without corruption.
另一方面，基于Web的邮件前端可以通过通用的 HTTP 协议 - 消息解码发生在远程服务器上。通过正常的 GET GET请求像其他图像一样检索图像。
Web-based mail front-ends, on the other hand, are accessed through the generic HTTP protocol - the message decoding happens at the remote server. Images are retrieved through normal GET requests like every other image.
几年前，您可能已经能够使用网络嗅探工具（例如 Wireshark的。最近体面的邮件提供商更喜欢这些协议（POP3S，IMAPS和 HTTPS ）的加密版本，哪些不能使用网络嗅探器进行有用的研究。
A few years back, you might have been able to see both cases at work using a network sniffer tool such as Wireshark. These days most decent mail providers prefer the encrypted versions of these protocols (POP3S, IMAPS and HTTPS) which cannot be usefully studied using a network sniffer.
如果您真的希望看到协议，您可能仍然可以找到允许的POP3 / IMAP服务未加密的连接，尽管它可能不会是一个大的提供商。您还可以设置您自己的服务器进行实验。
If you really wish to have a look at the protocols, you might still be able to find a POP3/IMAP service that allows unencrypted connections, although it's probably not going to be a big provider. You could also set-up your own server for experimentation.
另一方面，如果您使用 Firefox ，至少有一个附加组件，允许您可以通过在加密之前拦截请求来查看浏览器发出的请求。它将允许您查看如何使用例如Gmail。
If you use Firefox, on the other hand, there is at least one add-on that allows you to see the requests made by the browser, by intercepting the requests before they are encrypted. It will allow you to see what happens as you use e.g. Gmail.
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