Web: Web servers cooperate with Proxy servers to minimize network traffic and latency. Responsibility for consistency is taken by the proxy servers - they check the modification dates of pages frequently with the originating web server.
Mail: SMTP servers do not necessarily hold mail delivery routing tables to all destinations. Instead, they
simply route messages addressed to unknown destinations to another server that is likely to have the relevant tables.
Netnews: All NNTP servers cooperate in the manner described above to provide the newsfeed mechanism.
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