Servers perform different functions depending on the type of server. They manage networks and monitor all activities that go in and out the network. They can also be set up to secure networks and implement security policies to all users. Servers are called that because they "serve" client computers that make service requests to the server. Service requests can be accessing a website, sending or receiving emails or printing to a network printer.
A web server maintains and manages websites. Web browsers, like Internet Explorer, communicate to Web servers so that users can access different websites. Web servers define whether a website is internal or external. Internal website means that only those inside the network can access the website. External websites are made available to the Internet. Web servers are also responsible for ensuring that the connection between a computer and a website is secure. It provides different methods for authentication and stores security certificates.
Mail servers facilitate the sending and receiving of emails. Each email address has a mailbox that resides in a mail server. Mail servers send and receive emails through the Internet and sort the messages according to their email address destination. A user accesses a mailbox by using a mail user agent (MUA) such as Microsoft Outlook or other Web-based agent like Gmail or Yahoo mail. Mail servers implement policies such as determining whether an email is a junk mail and putting a limit on the storage capacity of each mailbox.
File and Application Servers
All files and applications in a network are stored and accessed through file and application servers. Depending on the network setup, users may have no actual files stored locally in their computers, because everything is placed in the file and application servers. These servers typically have many hard drives with large storage spaces to accommodate all the files and applications in the network. File and application servers make it easy to back up all of the data in a network.
A domain controller is the mastermind of all servers and computers in a network. It controls everything that goes in and out of the network, implements security policies and manages other servers as well. All other servers, before they can go out to the Internet, need to first pass through the domain controller. The domain controller provides the identity of a network. A domain, like google.com, stores all its information in a domain controller. Large networks usually have several domain controllers to handle all the workload.