【正文】 最后，從系統(tǒng)性能角度分析和設(shè)計了多種不同的信息過濾規(guī)則，使系統(tǒng)能夠適應(yīng)不同的應(yīng)用場合，滿足不同的需要。網(wǎng)絡(luò)信息過濾是根據(jù)一定的標(biāo)準(zhǔn)和利用一定的工具從動態(tài)的網(wǎng)絡(luò)信息流中選取相關(guān)信息或剔除無關(guān)信息的一系列過程。Pop全稱是郵局協(xié)議，是專門用于接收郵件的。而且用它的人數(shù)勢必會繼續(xù)增加。（1）它通常只在一個被信任的范圍里有效（2）它保護(hù)整個消息的封裝替，而不僅僅是正文（3）它鑒定消息的任務(wù)而不是消息的內(nèi)容（4）在發(fā)信者協(xié)同驗證下一個中轉(zhuǎn)點并且穿越一個合理的安全層級的情況下，它可以給發(fā)信者一個保證，那就是可以把消息安全地傳遞到下一個地點。一個消息的服務(wù)客戶端可能會要求用戶通過驗證，在任何它得到一個合適的SASL的時候。在SASL商議開始之前，任何協(xié)議之間的交互可以暢通無阻的進(jìn)行，但也有可能被活動著的攻擊者修改。排在上面的或者下面的被用來定義為有象征意義的字符串的用處僅僅是為了編輯時的便利以及清晰。538 請求的認(rèn)證機(jī)制需要加密這個響應(yīng)碼表示的是所選的認(rèn)證機(jī)制只有在簡單郵件傳輸協(xié)議連接在需要加密的情況下才能用454 暫時的認(rèn)證失敗這個響應(yīng)碼表示的是認(rèn)證失敗的原因是由于服務(wù)器暫時出現(xiàn)問題530 認(rèn)證是必須的除了認(rèn)證，EHLO，HELO，NOOP，RESET或者QUIT這幾個命令之外的任何一個命令，都將返回這個響應(yīng)碼。例如：C: 郵件來源:e=mc2 認(rèn)證=e+3Dmc2S: 250 OK錯誤代碼以下的錯誤代碼常常用來描述和標(biāo)識各種情況。如果認(rèn)證命令的可選的參數(shù)已經(jīng)提供了的話，不管是明確的提出還是由于前面段落的需要，服務(wù)器應(yīng)當(dāng)提供這個參數(shù)給任何其他支持認(rèn)證擴(kuò)展的用來中轉(zhuǎn)消息的服務(wù)器。如果服務(wù)器認(rèn)為最初提交消息的地址空間的客戶端是可信任的話，將會發(fā)出一個聲明，接著服務(wù)器應(yīng)當(dāng)提供一個相同的地址空間給任何其他支持認(rèn)證擴(kuò)展的用來中轉(zhuǎn)消息的服務(wù)器。一個Base64編碼的字符串通常來說是沒有長度限制的。客戶端的MUST命令將拋棄所有的從服務(wù)器獲得的認(rèn)知，例如不是通過SASL本身而獲得的簡單郵件傳輸協(xié)議服務(wù)擴(kuò)展的隊列。詳細(xì)說明這個SASL側(cè)面的服務(wù)器的名稱是“簡單郵件傳輸協(xié)議”。如果客戶端在認(rèn)證機(jī)制的認(rèn)證命令響應(yīng)中使用初始化建議，客戶端就在初始化命令中發(fā)送響應(yīng)的數(shù)據(jù)，服務(wù)器端用535回答來拒絕認(rèn)證命令。如果服務(wù)器接到這樣一個回應(yīng)，就通過發(fā)送一個501的響應(yīng)來拒絕執(zhí)行認(rèn)證命令。這種認(rèn)證機(jī)制的交互，由一系列的服務(wù)器的響應(yīng)和對認(rèn)證機(jī)制來說的一些特殊的回答來組成。討論：認(rèn)證命令顯示了一種和郵件服務(wù)器間的安全認(rèn)證機(jī)制 。諸如MUST, MUST NOT, SHOULD, SHOULD NOT, and MAY這些關(guān)鍵性的單詞被可以看作和“用在RFC文檔中用來標(biāo)示必須的級別的關(guān)鍵字” [KEYWORDS]相同的解釋。版權(quán)須知版權(quán)所有（1999年）Internet 團(tuán)體，所有權(quán)利將得到保留。簡單郵件傳輸協(xié)議稱為簡單Mail傳輸協(xié)議（Simple Mail Transfer Protocol），目標(biāo)是向用戶提供高效、可靠的郵件傳輸。進(jìn)程可能直接和其它進(jìn)程通過已知的IPCE通信。這種模式也就要求有不同的緩沖區(qū)來存儲這些對象，也就是說，有一個回復(fù)路徑緩沖區(qū)，一個轉(zhuǎn)發(fā)路徑緩沖區(qū)，一個郵件內(nèi)容緩沖區(qū)。下面討論簡單郵件傳輸協(xié)議命令和應(yīng)答。簡單郵件傳輸協(xié)議命令定義了郵件傳輸或由用戶定義的系統(tǒng)功能。如果簡單郵件傳輸協(xié)議接收者可以接收郵件則返回OK應(yīng)答。發(fā)送這個文檔是不受限制的。 help to improve the efficiency of access to information。s body.(3) It authenticates the message submission, not authorship of the message content(4) It can give the sender some assurance the message was delivered to the next hop in the case where the sender mutually authenticates with the next hop and negotiates an appropriate security layer.Additional security considerations are mentioned in the SASL specification [SASL].EMail plays a very important role in modern times. More and more people are using it, and the number of it will larger and larger. Though there are a lot of software for sending and receiving letters such as FoxMail which are also multifunctional, it is difficult and plicated to the Most of people who are curbstone. For this reason, we do this software with the rockbottom protocol of SMTP and Pop. The full name of SMTP is Simple Mail Transfer Protocol. It is used to sending letters. The full name of Pop is Post Office Protocol which is Special to receive letters. I basically take charge to how to realize the function of sending letters. A namespace which is named Mail Send is the soul of my includes two classes. A method named sundial which realize the function step by step belongs to the class of SmtpMail. It detailedly notes the track of client exchange to the server. You can use the software to send either a text E –mail or a texted Email with Attachments. You also can Send a letter to many addressee. In the nature of things, you can use a different SMTP service. The software I did support multiletters and multisender after I test. It is simplier than FoxMail and other professional softwares, but it is easy to hold and use.The rapid development of the Internet has to bee the world39。s taking effect, the SMTP protocol is reset to the initial state (the state in SMTP after a server issues a 220 service ready greeting). The server MUST discard any knowledge obtained from the client, such as the argument to the EHLO mand, which was not obtained from the SASL negotiation itself. The client MUST discard any knowledge obtained from the server, such as the list of SMTP service extensions, which was not obtained from the SASL negotiation itself (with the exception that a client MAY pare the list of advertised SASL mechanisms before and after authentication in order to detect an active downnegotiation attack). The client SHOULD send an EHLO mand as the first mand after a successful SASL negotiation which results in the enabling of a security layer.The server is not required to support any particular authentication mechanism, nor are authentication mechanisms required to support any security layers. If an AUTH mand fails, the client may try another authentication mechanism by issuing another AUTH mand.If an AUTH mand fails, the server MUST behave the same as if the client had not issued the AUTH mand.The BASE64 string may in general be arbitrarily long. Clients and servers MUST be able to support challenges and responses that are as long as are generated by the authentication mechanisms they support, independent of any line length limitations the client or server may have in other parts of its protocol implementation.Examples:S: 220 ESMTP server readyC: EHLO S: S: 250 AUTH CRAMMD5 DIGESTMD5C: AUTH FOOBAR