The LastUpdate property is used to specify the last date
and time that a list of newsgroups was retrieved from the server.
When this property is set, only those newsgroups created after that
date will be returned when the server is asked for a list of
groups. If this property is set to an empty string, then the server
will return all groups, regardless of when they were created.
This property should be used by client applications to reduce
the amount of time needed to update the list of available
newsgroups, particularly if the server offers a large number of
newsgroups. For example, the first time that the client connects to
the server, the LastUpdate property should not be set. That
will cause the server to return a list of all of the newsgroups
that it has available. The client should then store that list on
the local system in a file, and record the date and time that it
created the list. Then, the next time that the client connects to
the server, it should set the LastUpdate property to the
date that the local list of newsgroups was last updated. When the
list of newsgroups is requested again, the server will only return
those newsgroups that were created since the last time the list was
updated rather than the complete list.