email - "Message ID"电子邮件 header 对于每个收件人来说都是唯一的吗？

Question

电子邮件的消息 ID header 有多独特？如果我向两个人发送一封电子邮件，两人的消息 ID 是否相同？或者它们会有所不同吗？

(这是假设没有人在做任何有趣的事情。我知道对于垃圾邮件，所有规则都会失效......)

Answer 1

根据RFC2822 - Internet Message Format ，简短的回答是“消息 ID 应该对于消息的每个实例都是唯一的”；但是，MESSAGE-ID 字段被认为是可选的，并且 MESSAGE-ID 字段的创建方式取决于服务器。引用如下:

The "Message-ID:" field provides a unique message identifier that refers to a particular version of a particular message. The uniqueness of the message identifier is guaranteed by the host that generates it (see below). This message identifier is intended to be machine readable and not necessarily meaningful to humans. A message identifier pertains to exactly one instantiation of a particular message; subsequent revisions to the message each receive new message identifiers. Note: There are many instances when messages are "changed", but those changes do not constitute a new instantiation of that message, and therefore the message would not get a new message identifier. For example, when messages are introduced into the transport system, they are often prepended with additional header fields such as trace fields (described in section 3.6.7) and resent fields (described in section 3.6.6). The addition of such header fields does not change the identity of the message and therefore the original "Message-ID:" field is retained. In all cases, it is the meaning that the sender of the message wishes to convey (i.e., whether this is the same message or a different message) that determines whether or not the "Message-ID:" field changes, not any particular syntactic difference that appears (or does not appear) in the message.