[to] build a large capacity web-based email system

Building a large capacity web-based email system
Wangbo
In recent years, web-based free email systems have been very popular. At present, several famous free email websites have basically become the majority's choice, the establishment simply provides the free email service The site is no longer like before receives the warm welcome, but provides the web interface The email service has become one of the basic services which the commercial website provides for its registered member.
An email system can be divided into server and client, the Web interface of the email system is the email customers on the Web server side, so the email system needs to implement a Web interface email customers. However, because this email system requires a large number of users, so there are specific requirements for the email server.
Operating system and user databases
Because the provision of large capacity email system on the operating system and database requirements are very high, so the choice of the appropriate operating system and database is the most basic problem.
Because of the high stability and performance requirements of providing web and email services, UNIX is generally used as a server's operating system, for example, Hotmail uses FreeBSD and Solaris, and domestic 163 sites are also using the BSD series. However, Unix's standard email system is not suitable for this bulk service. Some UNIX systems, such as the current version of Linux, have a user ID of only 16 digits, so the number of users can only be 64k, even if the UNIX system itself supports a 32-bit user ID, the number of users supported by a single server does not exceed 100,000, given the performance factor.
In order to have the scalability to support more users, the general use of multiple servers at the same time to provide services, although still can use standard UNIX users as email users, but in view of security, performance and manageability, generally use non-UNIX system users as email users. While the user data is usually used to support the network Access database form, commonly used in the LDAP, standard database, and the email system to achieve their own user database. Among them, LDAP is the standard of providing directory service, so it should be the best choice, its common open source code is implemented as OPENLDAP, and the standard database is convenient and extensible, which is the most commonly used in MySQL on the internet, and there are other ways to implement it.
Save a message
For large capacity email system, the most critical technology is how to deal with the problem of mail storage, in which way to improve storage efficiency, will determine the success of the email system.
　　
Because of the large number of users, how to save the user's mail is a very important issue. Traditional UNIX uses a single directory to hold all users ' messages, which greatly reduces the performance of the file system when the number of users is large. Only a multi-level directory, a limited number of files per directory, can reduce the system consumption when opening files, or no longer use simple files to save messages, but in a certain package form. Completely take the database form to save the mail, because the user mail operation is many files operation, and the size change is big, therefore can cause the performance and the storage space bigger waste.