Comparison of Linux email server software

Linux Mail Server Software comparison-Linux Enterprise Application-Linux server application information, the following is a detailed description. A few years ago, only Sendmail was available for free mail servers in Linux. However, due to the Sendmail defect, some developers developed several other mail server software. Currently, the free email server running in Linux, or the MTA (Mail Transfer Agent), has several options: Sendmail, Qmail, Postfix, exim, and Zmailer. This article will describe the characteristics of MTA in mainstream Linux environments with relatively large impact, and analyze and compare their advantages and disadvantages one by one, this gives you a basis for choosing free MTA in Linux.

I. Postfix

Postfix is a product of a self-built software project developed by Wietse Venema, funded by IBM, to provide users with choice of email servers other than sendmail. Postfix is designed to be fast, easy to manage, and provide as much security as possible. It also tries its best to maintain compatibility with the sendmail mail server to meet users' usage habits. At first, the Postfix was published by the VMailer name, and later changed to Postfix for trademark reasons.

1. Main design objectives

The goal of the Postfix project is to implement an email server and provide users with options other than sendmail. Its design goals include:

Performance: Postfix is three times faster than similar Server products. A desktop with Postfix installed can send and receive millions of emails a day. The Postfix design uses web server design techniques to reduce Process Creation overhead, and uses other file access optimization techniques to improve efficiency, while ensuring software reliability.

Compatibility: the compatibility of Sendmail is considered during the design of Postfix to make it easier to transplant. Postfix supports/var [/spool]/mail,/etc/aliases, NIS, and ~ /. Forward and other files. However, to ensure the simplicity of management, Postfix does not support the configuration file sendmail. cf.

Security and robustness: the Postfix design enables the program to ensure the reliability of the process in case of excessive load. When the local file system has no available space or no available memory, the Postfix will automatically give up, instead of making the situation worse by retrying.

Flexibility: the Postfix structure consists of more than 10 small sub-modules. Each sub-module completes a specific task, such as receiving a message through SMTP protocol, sending a message, and passing a message locally, rewrite an address. When a specific requirement occurs, you can use a new version of the module to replace the old one without updating the entire program. In addition, it is easy to disable a function.

Security: Postfix uses multi-layer protection to prevent attackers from protecting the local system. Almost every Postfix daemon can run under a fixed chroot with low permissions, there is no direct path between the network and the security-sensitive local shipping program-an attacker must first break through several other steps to access the local system. Postfix does not even trust the content in its own queue file or IPC message to prevent spoofing. Postfix filters messages before outputting messages provided by the sender. In addition, the Postfix program does not have set-uid.

2. Postfix features

Supports multiple transmission domains: Sendmai supports message forwarding between the Internet, DECnet, X.400, and UUCP. Postfix is flexibly designed to implement such forwarding without virtual domain (vistual domai) or Alias. However, in the early release, only STMP was supported and UUCP was supported to a limited extent. However, for Chinese users, multi-transmission domain support was meaningless.

Virtual domain: In most general cases, adding support for a virtual domain only requires changing the Postfix query information table. Other mail servers usually require multiple levels of aliases or redirection to achieve this effect.

UCE control (UCE, unsolicited commercial email): Postfix can limit which host can forward mails by itself and which mails can be received. Postfix provides the following control functions: Blacklist list, RBL lookup, and HELO/sender DNS verification. Content-based filtering is not implemented currently.

Table view: Postfix does not implement the address rewriting language, but uses an extended table view to implement the address rewriting function. The table can be in local dbm or db file format.