Bruce Hagen wrote:

News servers only keep posts for a period of time. Each server is different.
MSNews keeps them for 90 days. Some servers keep them longer, some only for
a few days.

If you want to keep posts indefinitely, copy them to an OE local folder.

Also, make sure that in View | Current View, you have Show All Messages and
Group messages By Conversation checked and nothing else.

The reason regarding Bruce's reply is that OE remains in sync with the
NNTP server. If the NNTP server expires and drops a post then so, too,
will OE. You need to move items out of the newsgroups folder in OE if
you don't want them to get synchronized (i.e., deleted in OE after the
NNTP server deleted them).