According to RFC 3977, the Message ID of an article should be globally unique in the whole Usenet network.
I'm curious of how an NNTP server can ensure the global uniqueness of a Message ID when it allocates one.
I think my question can be further broken down into:
Who is responsible for creating the Message ID? The client posing the article or the NNTP server receiving the article from the posting client?
How does the program creating the Message ID ensure its global uniqueness across all Usenet servers? Is a Message ID conflict avoidable?
If a Message ID conflict is possible, how does the article propagation between two NNTP servers handle the situation? Does it mean two NNTP servers can have partitioned views of the article of the same Message ID but different body?