【正文】 ically valid AUTH parameters to the MAIL FROM mand and supply AUTH= parameters to any servers to which it authenticates using the AUTH extension.Examples:C: MAIL FROM : e=mc2 AUTH=e+3Dmc2S: 250 OK6. Error CodesThe following error codes may be used to indicate various conditions as described.432 A password transition is neededThis response to the AUTH mand indicates that the user needs to transition to the selected authentication mechanism. This typically done by authenticating that once using the PLAIN authentication Authentication mechanisms is too weak.This response to the AUTH mand indicates that the selected authentication mechanism is weaker than server policy permits for that user.538 Encryption required for requested authentication mechanismThis response to the AUTH mand indicates that the selected authentication mechanism may only be used when the underlying SMTP connection is encrypted.454 Temporary authentication failuresThis response to the AUTH mand indicates that the authentication failed due to a temporary server failure.530 Authentication requiredThis response may be returned by any mand other than AUTH, EHLO, HELO, NOOP, RSET, or QUIT. It indicates that server policy requires authentication in order to perform the requested action.7. Formal SyntaxThe following syntax specification uses the augmented BackusNaur Form (BNF) notation as specified in [ABNF].Except as noted otherwise, all alphabetic characters are case insensitive. The use of upper or lower case characters to define token strings is for editorial clarity only. Implementations MUST accept these strings in a caseinsensitive fashion.8. Security ConsiderationsSecurity issues are discussed throughout this memo. If a client uses this extension to get an encrypted tunnel through an insecure network to a cooperating server, it needs to be configured to never send mail to that server when the connection is not mutually authenticated and encrypted. Otherwise, an attacker could steal the client39。s profile of SASL is SMTP.If a security layer is negotiated through the SASL authentication exchange, it takes effect immediately following the CRLF that concludes the authentication exchange for the client, and the CRLF of the success reply for the server. Upon a security layer39。s Mail request to establish with the remote Mail server SMTP connection.Copyright NoticeCopyright (C) the Internet Society (1999). All Rights Reserved.1. IntroductionThis document defines an SMTP service extension [ESMTP] whereby an SMTP client may indicate an authentication mechanism to the server。 if you cannot receive, then refused to accept response to issue (but does not suspend operation of the entire message), the two sides will repeat so many times. When the recipients receive all messages will receive a special sequence, if the recipient of the message successfully processed, it returns OK response.SMTP mands define the mail transfer or by userdefined system functions. Its mand is CRLF End of the string. In the case with parameters, the mand itself is SP and the parameters separately, if not directly, and with parameters CRLF Connection. Mailbox syntax and receiving sites must be consistent with the form. SMTP mands and responses are discussed below. Send operations involving different data objects, their mutual connection by different parameters. Reply Path parameter is the MAIL mand, the forward path is the RCPT mand parameter, the message date is the DATA mand. These arguments or data objects must follow the mand. This model also requires a different buffer to store the objects, that is, there is a path back buffer, a forward path buffer, the contents of a message buffer. The mand generates its own specific buffer, or to one or more of the contents of the buffer is cleared.An important feature of SMTP is its ability to transmit messages in the Relay, Transfer Service provides interprocess munication (IPCE), and this environment may include a network, several networks or a network subnet. Understand that the transmission system (or IPCE) is not a one to one very important. Process and other processes may be directly through the munications of known IPCE. Mail is an application or interprocess munication. Mail can be connected in different IPCE the process of internetwork mail delivery. More specifically, mail can be a host of different network relay transmission.Known as the Simple Mail Transfer Protocol SMTP (Simple Mail Transfer Protocol), aim to provide efficient and reliable message transfer. An important feature of SMTP is its ability to transmit messages in the Relay, that the message can be different relay hosts on the network transmission. Work in two situations: First, transmission from the cl