電子郵件客戶端
出自KMU Wiki
1 電子郵件客戶端 ，又名郵件用戶代理 （ MUA ） ，又名電子郵件閱讀器是一個前端的計算機程序用來管理電子郵件 。
Sometimes, the term e-mail client is also used to refer to any agent acting as a client toward an e-mail server , independently of it being a real MUA, a relaying server, or a human typing directly on a telnet terminal.有時候，長遠的電子郵件客戶端 ，也是用來指任何代理人代理作為一個客戶對一個電子郵件服務器 ，獨立這是一個真正的mua ，中繼服務器，或者一個人打字，直接對Telnet工作終端。 In addition, a web application providing the relevant functionality is sometimes considered an email client.此外，在Web應用程序提供有關的功能，有時被視為一個電子郵件客戶端。
[ edit ] Retrieving messages from a mailbox [ 編輯 ] 檢索郵件從郵箱
Like most client programs, a MUA is only active when a user runs it.最喜歡的客戶端程序， mua只有積極當一個用戶運行。 Messages arrive on the Mail Transfer Agent (MTA) server.郵件到達在郵件傳輸代理 （ MTA ）服務器。 Unless the MUA has access to the server's disk, messages are stored on a remote server and the MUA has to request them on behalf of the user.除非MUA有訪問服務器的磁盤，信息存儲在遠程服務器和MUA有要求他們代表用戶。
In the first case, shared disk, a user logs on a server and runs a MUA on that machine.在首宗案件中，共享磁盤，用戶登錄服務器和運行一個mua關於該機器。 The MUA reads messages from a conventionally formatted storage, typically mbox , within the user's HOME directory.該mua讀取郵件從一個常規的格式儲存，通常mbox ，在用戶的主目錄。 The MTA uses a suitable Mail Delivery Agent (MDA) to add messages to that storage, possibly in concurrence with the MUA.該MTA使用一個合適的郵件派遞服務代理 （ MDA ）的添加信息的存儲，可能在同意與mua 。 This is the default setting on many Unix systems. Webmail applications running on the relevant server can also benefit from direct disk access to the mail storage.這是默認設置在許多UNIX系統。 郵局運行的應用程序就有關服務器可以受惠，同時也從直接磁盤訪問到的電子郵件貯存。
For personal computing, and whenever messages are stored on a remote system, a mail user agent connects to a remote mailbox to retrieve messages.用於個人計算的，每當郵件存儲在一個遙控系統，郵件用戶代理連接到一個偏遠的郵箱取回信件。 Access to remote mailboxes comes in two flavors.訪問遠程郵箱來分為兩種方式發行。 On the one hand, the Post Office Protocol (POP) allows the client to download messages one at a time and only delete them from the server after they have been successfully saved on local storage.就一方面， 郵局協議 （ POP ）允許客戶端下載郵件一在時間和只刪除它們從服務器後，他們已成功地保存在本地存儲。 It is possible to leave messages on the server in order to let another client download them.這是有可能在服務器上保留郵件，以便讓另一個用戶端將它們下載。 However, there is no provision for flagging a specific message as seen , answered , or forwarded , thus POP is not convenient for users who access the same mail from different machines or clients.不過，有沒有為標幟一個特定信息看 ， 回答 ，或轉發 ，因此， POP是不是方便了用戶誰獲得相同的郵件，從不同的機器或客戶。 On the other hand, the Internet Message Access Protocol (IMAP) allows users to keep messages on the server, flagging them as appropriate.在另一方面， Internet郵件訪問協議 （ IMAP ）允許用戶保持郵件在服務器上，標幟他們適當的。 IMAP provides sub-folders. IMAP的規定，子文件夾。 Typically, the Sent , Drafts , and Trash folders are created by default.通常情況下， 發送 ， 草稿和已刪除郵件文件夾默認情況下創建的。
Both POP and IMAP clients can be configured to access more mailboxes at the same time, as well as to check each mailbox every given number of minutes.雙方POP和IMAP客戶可以配置為獲取更多的信箱，在同一時間內，以及檢查每個信箱都給予的分鐘數。 IMAP features an idle extension for real time updates, that may work better than polling when long lasting connections are feasible. IMAP的功能閒置擴展的實時更新，可能更好地開展工作比投票站時，持久的聯繫，是可行的。
Client settings require the server's name or IP address , and the user name and password for each remote incoming mail box.客戶端設置需要服務器的名稱或IP地址 ， 用戶名和密碼，每個遠程來襲的信箱。
[ edit ] Formatting messages [ 編輯 ] 格式的郵件
Mail user agents usually have built-in the ability to display and edit text.郵件用戶代理通常有內置在能力來顯示和編輯文本。 Editing HTML text is a popular feature.編輯HTML文本是一個受歡迎的功能。 Invoking an external editor may be an alternative.引用外部編輯器可能是一個另類。
MUAs responsibilities include proper formatting according to RFC 2822 for headers and body , and MIME for non-textual content and attachments. muas的責任，包括適當的格式根據的RFC 2822為標題和身體 ，和MIME非文本的內容和附件。 Headers include the destination fields, To , Cc , and Bcc , and the originator fields From which is the message's author(s), Sender in case there are more authors, and Reply-To in case responses should be addressed to a different mailbox.標題包括目的地領域，消委會 ，並廣和領域從發端，這是郵件的作者（ s ）款， 發件人的情況下有更多的作者，並回复到在案件的反應，應給不同的郵箱。 To better assist the user with destination fields, many clients maintain one or more address books and/or are able to connect to an LDAP directory server.以更好地幫助用戶與目的地的領域，很多客戶保持一個或多個地址簿和/或無法連接到一個LDAP目錄服務器。 For originator fields, clients may support different identities.為發端領域，客戶端可能支持不同的身份。
Client settings require the user's real name and email address for each user's identity, and possibly a list of LDAP servers.客戶端設置需要使用者的真實姓名和電子郵件地址，為每個用戶的身份，並在可能的名單LDAP服務器。
[ edit ] Submitting messages to a server [ 編輯 ] 提交郵件服務器
As a basic function, a MUA is able to introduce new messages in the transport system.作為一項基本職能， mua是能夠引進新的郵件在運輸系統。 Typically, it does so by connecting to either an MSA or an MTA , two variations of the SMTP protocol.通常情況下，它這樣做是由連接到無論是生活津貼或MTA的 ，兩個變化SMTP協議。 The client needs to quickly put a message without worrying about where the message will be eventually delivered: that's why a transport system exists.客戶端的需求，迅速提出一個訊息，無需擔心那裡的信息，最終將發表的：這就是為什麼一運輸系統的存在。 Thus it always connects to the same preferred server.因此，它總是連接到相同的首選服務器。 However, how does that server know that it should accept and relay submissions from that client?不過，請問該服務器知道，它應該接受和中繼意見書，從客戶端？ There are two ways.有兩種方法。 The older method recognizes the client's IP address, eg because the client is on the same machine and uses internal address 127.0.0.1, or because the client's IP address is controlled by the same internet service provider that provides both internet access and mail services.舊方法確認客戶端的IP地址，例如，因為客戶端是在同一台機器上，並使用內部地址127.0.0.1 ，或因為客戶端的IP地址是由相同的互聯網服務供應商提供互聯網接入和電子郵件服務。 The newer method, since the SMTP protocol has an authentication extension, is to authenticate.較新的方法，因為SMTP協議有一個身份驗證擴展，是來驗證。 The latter method eases modularity and nomadic computing.後者的方法，簡化了模塊化和游牧計算。
Client settings require the name or IP address of the preferred outgoing mail server , the port number (25 for MTA, 587 for MSA), and the user name and password for the authentication, if any.客戶端設置規定的名稱或IP地址的首選外寄郵件伺服器 ， 連接埠號碼 （ 25的MTA ， 587為生活津貼） ，以及用戶名和密碼驗證，如果有的話。 There is a non-standard port 465 for SSL encrypted SMTP sessions, that many clients and servers support for backward compatibility. Transport Layer Security encryption can be configured for the standard ports, if both the client and the server support it.有一個非標準的端口465為SSL加密的SMTP會議上，許多客戶端和服務器的支持向後兼容。 傳輸層安全加密可配置為標準，港口，如果雙方在客戶端和服務器的支持。
[ edit ] Encryption [ 編輯 ] 加密
With no encryption, much like for postcards, email activity is plainly visible by any occasional eavesdropper. E-mail encryption enables to safeguard privacy by encrypting the mail sessions, the body of the message, or both.與沒有加密，很像為明信片，電子郵件活動，顯然是有形的任何偶爾eavesdropper 。 電子郵件加密 ，使以保障隱私加密的郵件，會議，郵件的正文，或兩者兼而有之。
[ edit ] Encryption of mail sessions [ 編輯 ] 加密的郵件會議
All relevant email protocols have an option to encrypt the whole session.所有相關的電子郵件協議有一個選項來加密整個會議。 Remarkably, those options prevent a user's name and password from being sniffed , therefore they are recommended for nomadic users and whenever the internet access provider is not trusted.值得注意的是，這些選項，防止用戶的名稱和密碼被sniffed ，因此，他們建議，游牧用戶和每當因特網接入提供者是不信任。 On sending mail, users can only control encryption at the hop from a client to its configured outgoing mail server .在發送郵件時，用戶只能控制加密在和合從客戶端，以通過其配置的外寄郵件伺服器 。 At any further hop, messages may be transmitted with or without encryption, depending solely on the general configuration of the transmitting server and the capabilities of the receiving one.在任何進一步的酒花，郵件可能會轉交有或沒有加密，這取決於單就一般的配置，傳輸和服務器的能力，接收1 。
Encrypted mail sessions deliver messages in their original format, ie plain text or encrypted body, on a user's local mailbox and on the destination server's.加密郵件會議提供的信息在其原來的格式，即純文本或加密的機構，對用戶的本地郵箱和對目標服務器的。 The latter server is operated by an email hosting service provider, possibly a different entity than the internet access provider currently at hand.後者是服務器所經營的電子郵件託管服務提供商，可能是不同的實體，比因特網接入供應商，目前在手。
[ edit ] Encryption of the message body [ 編輯 ] 加密的郵件正文
There are two models for managing cryptographic keys. S/MIME employs a model based on a trusted certificate authority (CA) that signs users' public keys. OpenPGP employs a somewhat more flexible web of trust mechanism that allows users to sign one another's public keys.有兩種模式管理加密鑰匙。 S / MIME的僱用了模型的基礎上，受信任的證書頒發機構 （ CA ）表示，跡象用戶的公開密碼匙。 openpgp僱用了一些更靈活的網絡信任機制，允許用戶註冊一個另一個的公開密碼匙。 OpenPGP is also more flexible in the format of the messages, in that it still supports plain message encryption and signing as they used to work before MIME standardization. openpgp也更靈活，在格式的郵件，因為它仍然支持平原信息的加密和簽字，因為他們用於工作之前， 默劇標準化。
In both cases, only the message body is encrypted.在這兩種情況下，只有郵件正文是加密。 Headers, including originator, recipients, and subject, remain in plain text.標題，包括發端，收件人，主題，繼續留在純文本。
[ edit ] Standards [ 編輯 ] 標準
While popular protocols for retrieving mail include POP3 and IMAP4 , sending mail is usually done using the SMTP protocol.而受歡迎的協議檢索郵件，包括POP3和IMAP4 ，發送郵件通常是使用SMTP協議。
Another important standard supported by most e-mail clients is MIME , which is used to send binary file e-mail attachments .另一個重要的標準，支持大部分電子郵件客戶端是默劇 ，這是用來傳送二進制文件的 電子郵件附件 。 Attachments are files that are not part of the e-mail proper, but are sent with the e-mail.附件的文件是不是部分的電子郵件正確，但與發送電子郵件。
Most e-mail clients use an X-Mailer header to identify the software used to send the message.大多數電子郵件客戶端使用的X郵件的標題 ，以確定使用的軟件來發送該信息。 According to RFC 2076 , this is a common but non-standard header.據的RFC 2076 ，這是一個共同但有非標準的標題。
RFC 4409 , Message Submission for Mail , details the role of the Mail submission agent . 符合RFC 4409 ， 信息提交的郵件 ，細節的作用， 郵件提交代理 。
RFC 5068 , Email Submission Operations: Access and Accountability Requirements , provides a survey of the concepts of MTA, MSA, MDA, and MUA. 符合RFC 5068 ， 電子郵件提交作業：准入和問責制的要求 ，提供了調查的概念的MTA ，生活津貼，丙二醛，和mua 。 It mentions that " Access Providers MUST NOT block users from accessing the external Internet using the SUBMISSION port 587 " and that " MUAs SHOULD use the SUBMISSION port for message submission. "它提到， “ 接入服務提供商必須不能阻止用戶訪問外部的互聯網使用提交港口587 ”和“ muas應使用提交港口的訊息，提交 ” 。
[ edit ] Port numbers [ 編輯 ] 連接埠號碼
TCP port numbers for email default as follows: TCP端口號碼，電子郵件默認如下：
protocol議定書 use使用 plain text or encrypt sessions純文字或加密會議 plain text sessions only純文字的會議只 encrypt sessions only加密會議只
POP3 的POP3 incoming mail收郵件 110 995
IMAP4 的IMAP4 incoming mail收郵件 143 993
SMTP 的SMTP outgoing mail外寄郵件 25 (unofficial) 465 （非官方） 465
MSA 生活津貼 outgoing mail外寄郵件 587
HTTP 的HTTP webmail郵局 80 443
[ edit ] Webmail [ 編輯 ] 的Webmail
In addition to the fat client e-mail clients and small MUAs, there are also Web -based e-mail programs called webmail .此外，向客戶發電子郵件客戶端和小muas ，也有基於Web的電子郵件程序所謂的Webmail 。 Webmail has several advantages which include the ability to send and receive e-mail from anywhere using a single application: a web browser.郵局有幾大優點，其中包括能夠發送和接收電子郵件從任何地方使用一個單一的應用程序： Web瀏覽器。 This eliminates the need to configure an email client.這消除了需要配置一個電子郵件客戶端。 Significant examples of e-mail services which also provide the user a webmail interface are Hotmail , Gmail and Yahoo .顯著的例子，電子郵件服務，也為用戶提供一的Webmail界面的Hotmail ， Gmail和雅虎 。 The main drawbacks of webmail are that user interactions are subject to network response and that there is no offline capability.主要缺點的Webmail是用戶交互受到網絡響應，並沒有離線的能力。 For instance, while webmail generally provides the best experience over broadband, a fat client can provide a satisfactory experience over dialup, and messages can be searched and viewed without an internet connection.舉例來說，一般的Webmail提供了最佳的經驗，寬帶，一個胖客戶端可以提供令人滿意的經驗，撥號，信息可以被搜查，並認為沒有一個網際網路連線。
資料引用:[1]
