Cross-posting is a practice of sending the same message to multiple Usenet newsgroups or mailing lists. When a message is cross-posted, it is delivered to all the groups or lists that have been included in the message header. This can cause some reading problems on NNTP servers, where the message might appear multiple times or not at all, depending on the configuration of the server and the client.
To diagnose cross-posted message reading problems, you need to understand how NNTP servers handle cross-posted messages. When a message is posted to multiple newsgroups, the server should store only one copy of the message and create a cross-reference or pointer to that message for each newsgroup. When a user requests to read the message in one of the newsgroups, the server should look up the cross-reference and deliver the message content to the user.
However, some servers may be configured to duplicate the message for each newsgroup, which can result in the same message appearing multiple times to users who read more than one of the newsgroups. In other cases, the server may fail to create the cross-reference or pointer correctly, causing the message to be missing or inaccessible in some newsgroups.
To diagnose these issues, you can use tools such as NNTP clients or newsreaders that allow you to view the headers and body of the messages, as well as the list of newsgroups they are posted to. You can compare the headers of the same message in different newsgroups to see if they are identical or different. You can also check the server configuration to see if it is set up to handle cross-posted messages correctly.
In summary, diagnosing cross-posted message reading problems on an NNTP server requires understanding how the server handles cross-referencing and duplication, and using tools to compare the headers and body of the messages across different newsgroups.
