【正文】 request to determine whether this local mail, if sent to the user39。 can reduce unnecessary transmission of information so that the network more smoothly。發(fā)送郵件操作涉及到不同的數(shù)據(jù)對象，它們由不同的參數(shù)相互連接。簡介這個文檔定義了簡單郵件傳輸協(xié)議服務(wù)的擴(kuò)展（E簡單郵件傳輸協(xié)議）并且說明了一個簡單郵件傳輸協(xié)議客戶端可以為服務(wù)器指定一種用來執(zhí)行與認(rèn)證協(xié)議的交換，并且隨意地穿越并發(fā)的協(xié)議之間交互的安全層面的認(rèn)證機(jī)制。對認(rèn)證命令來說，可選的初始化響應(yīng)建議是用來在使用認(rèn)證機(jī)制時保持一個往返的回程,認(rèn)證機(jī)制的定義中此建議不發(fā)送任何數(shù)據(jù)。只要由認(rèn)證機(jī)制產(chǎn)生的受客戶端和服務(wù)器支持的命令和響應(yīng)，客戶端和服務(wù)器端須支持，而不依賴于服務(wù)器或者客戶端的、可能存在于協(xié)議實(shí)現(xiàn)的某些方面的行長度的限制。這表示服務(wù)器需要為了執(zhí)行被請求的操作，需要一個認(rèn)證。另外需要說明的是，安全問題的考慮在SASL說明里面也有提到。越來越多的人在使用它。除了那些被標(biāo)注的以外，所有的按字母順序排列的特征都是適合于固定場合的。討論：認(rèn)證中一個可選的參數(shù)的郵件來源 命令允許一個協(xié)同工作的代理與一個單獨(dú)的消息就行通信在一個被信任的環(huán)境里。它發(fā)送一個零長度的初始化回答作為一個=符號。這個文檔用到的協(xié)定在以下的這些例子中，C和S分別表示客戶端和服務(wù)器。這些參數(shù)或者數(shù)據(jù)對象必須跟在命令后。說到這，為了標(biāo)準(zhǔn)化這個協(xié)議的狀態(tài)和地位，就必須提及目前最新的“Internet 官方協(xié)議的標(biāo)準(zhǔn)”(STD1)。 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 client to the server。s knowledge。而在帶有參數(shù)的情況下，命令本身由SP和參數(shù)分開，如果未帶參數(shù)可以直接和CRLF連接。工作在兩種情況下：一是電子郵件從客戶機(jī)傳輸?shù)椒?wù)器；二是從某一個服務(wù)器傳輸?shù)搅硪粋€服務(wù)器?？蛻舳说幕貞?yīng)是一個包含Base64編碼的字符串的隊(duì)列。服務(wù)器不一定要求支持任何的認(rèn)證機(jī)制，而認(rèn)證機(jī)制也不一定要支持所有的安全層。比較由代表性的就是一旦你使用了PLAIN認(rèn)證機(jī)制的話，就必須進(jìn)行轉(zhuǎn)換。這個擴(kuò)展并不是有意的取代或者被用來取代端到端的消息簽名在加密系統(tǒng)S/MIME或者PGP中。本文通過對信息過濾一般過程的分析，將信息過濾中的相關(guān)技術(shù)引入到網(wǎng)絡(luò)安全領(lǐng)域。因此，我們就利用簡單郵件傳輸協(xié)議和郵局協(xié)議從底層開發(fā)了這個軟件。安全問題考慮如果客戶端使用這個擴(kuò)展得到不加密的渠道但是通過一個不安全的網(wǎng)絡(luò)連接到協(xié)同工作的服務(wù)器的話，客戶端將被阻斷而永遠(yuǎn)不能發(fā)送郵件到服務(wù)器，當(dāng)服務(wù)器不能夠互助地進(jìn)行驗(yàn)證和加密的時候。如果服務(wù)器不是充分的相信客戶端的身份或者客戶端并沒有得到認(rèn)證的話，那么服務(wù)器必須自己提供認(rèn)證命令的那個參數(shù)一個值。如果服務(wù)器拒絕認(rèn)證的數(shù)據(jù)，服務(wù)器應(yīng)該拒絕執(zhí)行并返回一個535響應(yīng)碼除非有更詳細(xì)的錯誤代碼，例如在Section 6列出來的那個。在成功執(zhí)行了一個認(rèn)證命令之后，服務(wù)器必須拒絕后來的認(rèn)證命令并且返回一個503響應(yīng)碼。簡單郵件傳輸協(xié)議的一個重要特點(diǎn)是它能夠在傳送中接力傳送郵件，傳送服務(wù)提供了進(jìn)程間通信環(huán)境（IPCE），此環(huán)境可以包括一個網(wǎng)絡(luò)，幾個網(wǎng)絡(luò)或一個網(wǎng)絡(luò)的子網(wǎng)。具體工作方式為：發(fā)送簡單郵件傳輸協(xié)議在接到用戶的郵件請求后，判斷此郵件是否為本地郵件，若是直接投送到用戶的郵箱，則向 DNS查詢遠(yuǎn)端郵件服務(wù)器的MX紀(jì)錄，并建立與遠(yuǎn)端接收簡單郵件傳輸協(xié)議之間的一個雙向傳送通道，此后簡單郵件傳輸協(xié)議命令由發(fā)送簡單郵件傳輸協(xié)議發(fā)出，由接收簡單郵件傳輸協(xié)議接收，而應(yīng)答則反方面?zhèn)魉汀?perform an authentication protocol exchange, and optionally negotiate security layer for subsequent protocol interactions. This extension is a profile of the Simple Authentication and Security Layer [SASL].2. Conventions Used in this DocumentIn examples, C: and S: indicate lines sent by the client and server respectively. The key words MUST, MUST NOT, SHOULD, SHOULD NOT, and MAY in this document are to be interpreted as defined in Key words for use in RFCs to Indicate Requirement Levels [KEYWORDS].3. The Authentication service extension(1) The name of the SMTP service extension is Authentication(2) The EHLO keyword value associated with this extension is AUTH(3) The AUTH EHLO keyword contains as a parameter a space separated list of the names of supported SASL mechanisms.(4) A new SMTP verb AUTH is defined(5) An optional parameter using the keyword AUTH is added to the MAIL FROM mand, and extends the maximum line length of the MAIL FROM mand by 500 characters.(6) This extension is appropriate for the submission protocol [SUBM