mail system

Definition of mail system in The Network Encyclopedia.

What is Mail System?

Any set of applications used to support e-mail messaging between a group of users in an organization or between users in different organizations. Mail systems include both client software (for composing, sending, receiving, and viewing messages) and server software (for storing and transporting messages).

How Mail System works?

Mail systems come in two general types:

  • Shared-file mail systems:
    The client software initiates and maintains all messaging activity. The server is a passive file server (usually called a postoffice). The client regularly polls the server for new messages, and if messages are found, the client downloads and displays them. An example of a shared-file mail system is Microsoft Mail. Advantages of such mail systems include low server-end requirements and simple maintenance. Disadvantages include limited security, high processing load for the client, and poor scalability.


  • Client/server mail systems:
    The client makes requests to the server, and the server processes the requests, either receiving mail from the client or sending mail to the client. The client and the server share the processing of messages. An example of a client/server mail system is Microsoft Exchange Server, which uses remote procedure calls (RPCs) for communication between clients and servers. Advantages of client/server mail systems include lower network traffic, scalability, and security. The main disadvantage is that they require more powerful servers than shared-file mail systems do.



Mail systems are also distinguished by their address formats. Each mail system uses one or more address formats. These can be industry-standard formats such as the Simple Mail Transfer Protocol (SMTP) or X.400 standard Originator/Recipient (O/R) format, or they can be proprietary address formats such as the Microsoft Mail version 3 or Lotus cc:Mail format. Exchange Server supports most popular industry-standard and proprietary address formats. The following table lists some of the address formats supported by Exchange.

Address Formats Supported by Exchange

Address Format Example
X.400 O/R
Microsoft Mail
Tulloch, Mitch at northwind

Exchange Server can offer an all-in-one mail system solution because it can provide messaging connectivity with legacy mail systems such as Microsoft Mail and foreign mail systems such as Lotus cc:Mail, Internet SMTP mail, and X.400 messaging systems. This connectivity is provided by connectors such as the X.400 Connector and Internet Mail Service. You can thus use Exchange as a messaging backbone system in a heterogeneous mail system environment. Exchange Server also includes the Microsoft Exchange Migration Wizard, which you can use to migrate users and mailboxes from legacy and foreign mail systems to an Exchange-based system. This migration can simplify administration and reduce costs.