![RFC5321“接收方应检查[...]回复代码”（为什么？）](https://linux22.com/image/647581/RFC5321%E2%80%9C%E6%8E%A5%E6%94%B6%E6%96%B9%E5%BA%94%E6%A3%80%E6%9F%A5%5B...%5D%E5%9B%9E%E5%A4%8D%E4%BB%A3%E7%A0%81%E2%80%9D%EF%BC%88%E4%B8%BA%E4%BB%80%E4%B9%88%EF%BC%9F%EF%BC%89.png)
在 SMTP 中，所有以数字开头的commands邮件均由 发送。senderresponsescodereceiver
但还有一点：
RFC5321第4.2节
Whenever possible, a receiver-
SMTP SHOULD test the first digit (severity indication) of the reply
code.
嗯？这是 RFC 中的错误吗？他们的意思是sender而不是 吗receiver？
下一段他们说sender。
Consequently, a sender-SMTP MUST be prepared to handle codes not
specified in this document and MUST do so by interpreting the first
digit only.
这句话很有道理，
答案1
在我看来，这似乎是打字错误。提交勘误表。