RFC 1870: SMTP Service Extension ...
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client and server


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... SMTP service whereby an SMTP client and server may interact to give the server an opportunity to decline to accept a message (perhaps temporarily) based on the client ...


... The remainder of this memo specifies how support for the extension affects the behavior of an SMTP client and server. ...


... transmitting the entire message to the server (which discards the transferred message). If, however, both client and server support the Message Size Declaration service ...



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