Chapter XV using Postfix and Dovecot-premises messaging system
E-mail system
E-mail system based on e-mail protocol to complete the transfer of e-mail, common mail protocol have the following:
Simple Mail Transfer Protocol ( 25 / TCP port used to send e-mail and transit issued occupancy server: Simple Mail Protocol, SMTP).
Post Office Protocol version 3 (Post Office Protocol 3): used to store e-mail to the local host, occupying server 110 / TCP port.
Internet Message Access Protocol version 4 (Internet Message Access Protocol 4): used to access e-mail access on the local host, occupying server 143 / TCP port.
When you deploy enterprise-class e-mail system in a production environment, there are four considerations Please note:
Anti-spam and anti-virus module add: it can be very effective to prevent spam or virus messages interference with business mail.
Mail encryption: can effectively protect the message content from being stolen and altered by hackers.
Add mail monitoring audit modules: Mail the staff can effectively monitor the company if it contains sensitive words, if there are irregularities revealed enterprise information.
Safeguard stability: stability is critical email systems, operation and maintenance personnel should be done to ensure the stable operation of the e-mail system, and in a timely manner to prevent distributed denial (service Service, DDoS Distributed Denial of) ready to attack.
Chapter XVI use Squid proxy cache deployment services
Proxy caching services
Squid is the most popular Linux system, a high-performance proxy service software, Web sites usually used as pre-caching service, the user can request instead of page data to the server and cached.
Squid service program has a simple configuration, high efficiency, feature-rich features, it supports data caching multiple protocols HTTP, FTP, SSL, etc., can be based on the access control list (ACL) and access lists (ARL) to perform content filtering and rights management, can also be based on a variety of conditions prohibit users from accessing the site there is a threat or inappropriate resources, thereby protecting the enterprise network security, improve the user's web experience, to help save network bandwidth.
In use when the service program Squid caching proxy service to provide users with a forward proxy mode and sub-mode of the reverse proxy.
The so-called forward proxy mode, refer to allow users to get service program Squid web pages and other resources, as well as the access control list (ACL) function to restrict user access to the site behavior, in particular the way the service is divided into standard and proxy mode transparent proxy mode. Standard mode is put forward proxy cache server data to a local site, improve the efficiency of resource data is accessed again, but the user must fill in the proxy server IP address and port number information in a browser and other software in the Internet, the default is not otherwise use a proxy service. Forward proxy mode and transparent effects standard forward proxy mode is basically the same, except that the user does not need to manually specify the proxy server's IP address and port number, so that the proxy services for users but is relatively transparent.
Reverse proxy mode means that allows multiple hosts reverse caching node site data, thus speeding user access speed. Because in general, the site will generally load a lot of text, images and other static resources, but they are relatively more stable data when the user initiates a web page to access these static resource requests, we can use Squid reverse proxy mode service program provides to respond. Moreover, if the reverse proxy server happens to have a static resource to be accessed by the user, it will be sent directly to cache these static resources to the user, which can not only speed up the user's site access speed, reducing the server also to some extent load pressure.
If you want to know more, you can go to the website ( https://www.linuxprobe.com ) Download the " Linux in respect of such a study" electronic version of the book.
Here are some study notes:
