* Introduction to several mail servers in the nix Environment

Below we will introduce several frequently-used mail server software products for your reference.
1. Sendmail in Unix environment

Sendmail is a very good software, regardless of its wide application or Code complexity. If you use it to build a website's email system, you don't have to worry about it, because this software is built in almost all Unix default configurations, you just need to set up the operating system, it can run immediately. In Unix systems, Sendmail is the most widely used email server. It is a free software that supports thousands or more users and occupies quite a few system resources.
However, the Sendmail system structure is not suitable for large loads. for High-load mail systems, you need to make complex adjustments to Sendmail.
2. Postfix and Qmail in Linux

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. Postfix uses multi-layer protection to prevent attackers from protecting the local system. Postfix is three times faster than similar Server products. A desktop with a 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 other file access optimization techniques to improve efficiency, while ensuring software reliability. Postfix is designed to be a replacement for Sendmail. For this reason, many parts of the Postfix system, such as local shipping programs, can be easily replaced by editing and modifying configuration files similar to inetd.

Qmail is divided into different modules according to the system, which are responsible for receiving external emails and for managing the mail queues to be sent in the buffer directory, the principle of sending emails to remote servers or local users is designed. Qmail aims to solve the security problem of sendmail, and the entire system structure is redesigned. Security issues are particularly considered in the design and implementation. The configuration of Qmail is inconsistent with that of Sendmail, so it is not easy to maintain. In addition, Qmail's copyright license has a vague meaning and is not even released together with the software.

The modular design method based on the Unix idea enables Qmail to have high performance. Qmail also provides some very useful features to enhance the reliability of the system. In addition, Qmail also has some very unique features, it not only provides Sendmail-compatible methods for forwarding, alias, and other capabilities, but also supports Sendmail in completely different ways to provide these functions.

3. SUN's iPlanet Messaging Server

IPlanet Messaging Server is a powerful, reliable, and large-capacity Internet mail Server designed for enterprises and service providers. Messaging Server uses a centralized LDAP database to store user, group, and domain information. It supports standard protocols, multiple domain names, and Webmail, with powerful security and access control.

As an open and scalable Internet-based high-performance telecom-level communication platform, iPlanet Messaging Server supports tens of millions of users. Its main features include authorization management, virtual host and virtual domain, which are powerful and easy to expand. Operators will benefit from the value-added services provided by their integrated information service systems, including email, wireless technology, and integrated information.

4. IBM Domino Mail Server

The Domino Mail Server provides a unified architecture that can be used for email, Web access, online calendar and group calendar, collaborative workspace, bulletin board, and newsgroup services. From Lotus Notes to Web browsers, to Outlook and PDA, the unparalleled mobile functions and support for a wide range of clients enable users to send and receive information securely anytime, anywhere.

The Domino Mail Server can run on the existing hardware, software, and network of the enterprise, and achieve seamless interoperability with other communication systems through open standards. Centralized desktop control, information tracking and monitoring, and remote server management can provide stable IT support for regional offices, further reducing the cost of ownership. Optimized additional products such as desktop fax and integrated document management programs can increase system value and expand the enterprise's communication infrastructure.