　　企业邮箱作为一种越来越广泛的应用而被更多企业用户使用。传统的webmail收发邮件的方式，在于更多的企业用户来讲，利用outlook、foxmail等客户端收发邮件显得更为广泛。一方面，是由于企业用户的信件量比较大，客户端的收发在办公文档的处理与邮件的回复查阅方面更加便捷，桌面化的操作省去了不少时间，提高了工作效率；另一方面，对于企业用户来讲，往来的商务信函，更需要一个妥善的保管与保存，于是，客户端的收发就显得尤为重要。免费众多的企业邮箱产品，或者已经确定的企业邮箱产品，企业用户改选择怎样的邮件收发协议呢？

　　一、让我们从最常用的smtp、pop3开始！

　　先让我们了解一下，这两种协议的定义。

　　SMTP(Simple Mail Transfer Protocol)即简单邮件传输协议，它是一组用于由源地址到目的地址传送邮件的规则，由它来控制信件的中转方式。SMTP协议属于TCP／IP协议族，它帮助每台计算机在发送或中转信件时找到下一个目的地。通过SMTP协议所指定的服务器，我们就可以把E－mail寄到收信人的服务器上了，整个过程只要几分钟。SMTP服务器则是遵循SMTP协议的发送邮件服务器，用来发送或中转你发出的电子邮件。

　　POP3(Post Office Protocol 3)即邮局协议的第3个版本，它规定怎样将个人计算机连接到Internet的邮件服务器和下载电子邮件的电子协议。它是因特网电子邮件的第一个离线协议标准，POP3允许用户从服务器上把邮件存储到本地主机（即自己的计算机）上，同时删除保存在邮件服务器上的邮件，而POP3服务器则是遵循POP3协议的接收邮件服务器，用来接收电子邮件的。

　　利用outlook收发邮件的用户都知道，通过pop与smtp的设置，可以把webmail页面的收件箱的邮件都收到自己的本地机器上，同时，我们还可以做“是否在邮件服务器上保留副本”的设置。大大的方便了企业邮箱的用户收发邮件。

　　二、Imap4协议已被更多企业用户选择！

　　1、什么是Imap协议？

　　IMAP是Internet Message Access Protocol的缩写，顾名思义，主要提供的是通过Internet获取信息的一种协议。IMAP4是IMAP协议的第4个版本，正如POP3是POP 协议的第3个版本一样。在21cn.com邮件系统内，IMAP是一种强有力的邮箱访问方式。

　　2、和POP3的区别

　　由于很多用户都对POP3非常熟悉，我们就从POP3说起。POP3提供了快捷的邮件下载服务,用户可以利用POP3把邮箱里的信下载到PC上进行离线阅读。一旦邮件进入PC的本地硬盘，就可以选择把邮件从服务器上删除，然后脱离与Internet的连接并选择在任何时候阅读已经下载的邮件。

　　IMAP同样提供了方便的邮件下载服务，让用户能进行离线阅读，但IMAP能完成的却远远不只这些。首先，IMAP提供的摘要浏览功能可以让你在阅读完所有的邮件到达时间、主题、发件人、大小等信息后才作出是否下载的决定。也就是说，你不必等所有的邮件都下载完毕后才知道究竟邮件里都有些什么。如果你根据摘要信息就可以决定某些邮件对你毫无用处，你就可以直接在服务器上把这些邮件删除掉，而不必浪费你宝贵的上网时间。如果你的IMAP客户端软件完整支持 IMAP4rev1的话(如Netscape 4.5)，则你还可以享受选择性下载附件的服务。举例来说，假如一封邮件里含有大大小小共5个附件，而其中只有2个附件是你需要的，你就可以只下载那两个附件，节省了下载其余3个的时间。

　　3、和WebMail的比较

　　也有很多用户喜欢通过Web来联机收发邮件，其中一个很重要的原因是这些用户希望把他的邮件都留在服务器上，并且通过WebMail服务建立多个文件夹，然后分类归档地管理自己的邮件。这样，WebMail的用户就可以不分时间地点，只要有一个浏览器就可以马上从服务器上获得自己的邮件，不管是刚收到的还是已经存放了很久，也不必担心客户端的PC重新安装了操作系统或换了一台电脑以后邮件全部丢失了的问题。

　　IMAP同样满足了WebMail用户的需要。IMAP与POP3不同的地方关键是在支持离线阅读的同时也鼓励用户把邮件存储和组织在服务器上。和 WebMail一样，通过IMAP，允许用户在服务器上建立任意层次结构的文件夹，并且可以灵活地在文件夹之间移动邮件，随心所欲地组织你的邮箱(这些显然是通过POP3做不到的)。只要你的邮件存储在服务器上，任何时候通过一个IMAP的客户端软件都可以立即联机获得你的邮件，这一点与WebMail保持一致，但是，IMAP的以下优点足以把WebMail用户吸引过来：凡是WebMail的用户都必需无奈地阅读页面上的广告，都必需花费宝贵的时间和带宽来下载页面上的图面，修饰字符等等；IMAP则忠实地只为你的Email服务，不让你的资源有丝毫的浪费。

　　IMAP协议还允许你方便地利用你的邮箱作为信息存储工具，一般的IMAP4客户软件都支持邮件在本地文件夹间和服务器文件夹间的随意拖动，让你得心应手地把本地硬盘上的文件存放到服务器上，然后在你需要的时候同样方便地取回来，所有的功能仅需要一次鼠标拖放的操作来实现，是不是很好？

　　总的来说，POP3和WebMail的优点在IMAP里都有，而IMAP却能很好地克服POP3和WebMail各自的缺点。

[#page_是否还有其他收发协议#0#0#0#0#]

　　三、除了Imap4协议，是否还有其他的企业邮箱收发协议？

　　答案是肯定的。

　　1、ESMTP，英文全称是“Extended SMTP”，顾名思义，扩展SMTP就是对标准SMTP协议进行的扩展。它与SMTP服务的区别仅仅是，使用SMTP发信不需要验证用户帐户，而用 ESMTP发信时，服务器会要求用户提供用户名和密码以便验证身份。验证之后的邮件发送过程与SMTP方式没有两样。

　　2、对应的EPOP3，（Encrypted POP3）即加密下载电邮协议。

　　3、SSL邮件加密协议。SSL 的英文全称是 “Secure Sockets Layer” ，中文名为 “ 安全套接层协议层 ” ，它是网景（ Netscape ）公司提出的基于 WEB 应用的安全协议。 SSL 协议指定了一种在应用程序协议（如 HTTP 、 Telenet 、 NMTP 和 FTP 等）和 TCP/IP 协议之间提供数据安全性分层的机制，它为 TCP/IP 连接提供数据加密、服务器认证、消息完整性以及可选的客户机认证。

　　在设置邮件加密协议的同时，接收邮件的端口号与发送邮件的端口号已经不是25与110端口，一般的企业邮箱厂商会针对此类设置有所说明，同时，也并不是所有的企业邮箱都支持ssl的客户端设置。

　　4、TLS：安全传输层协议（TLS：Transport Layer Security Protocol）安全传输层协议（TLS）用于在两个通信应用程序之间提供保密性和数据完整性。该协议由两层组成： TLS 记录协议（TLS Record）和 TLS 握手协议（TLS Handshake）。较低的层为 TLS 记录协议，位于某个可靠的传输协议（例如 TCP）上面。出于安全性的考虑，现在也有部分用户在使用支持tls协议的企业邮箱进行邮件收发。

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