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.