Article: How LAN-based E-mail Interfaces with the Network

Many issues arise in a cc:Mail system because the system is not properly deployed over file servers and networks. This happens because implementers are not always aware of how the cc:Mail system works. Rather than delving into the workings of the cc:Mail database this article focuses instead on the relationship of cc:Mail systems to the networks they run on.

cc:Mail System Component Overview

A cc:Mail system consists of e-mail applications for users, back-end communications software, and administrative tools. These software components work together in a network to integrate various types of end-user workstations into a cross-platform cc:Mail system. There are just a few basic components.

All cc:Mail systems, regardless of the number of users, have at least a post office, user mail applications and administrative software. If the post office exchanges messages with other post offices or other types of e-mail systems, it may also have one or more cc:Mail Routers or e-mail gateways such as Link to SMTP. For cc:Mail version 8 and above, the system may also include various servers, such as cc:Mail for the World Wide Web or the cc:Mail R8 IMAP4 Server.

The cc:Mail system (apart from the version 8 servers) works in an Open Systems Interconnect (OSI) model network. The OSI model defines an open, hardware-independent system of networking where application programs do not need to concern themselves with lower layers of the network. Most methods for providing access to files over a network are generally described by the OSI model.

How cc:Mail Interfaces with the Network

Accessing and sharing files over a network involves software components on both file servers and workstations. In an OSI LAN, application software does not necessarily have to support specific network hardware or protocols in order to access information over a network. Together, software components on workstations and file servers that provide transparent access to files for applications make up the network operating system. Examples of network operating systems, include Novell NetWare, Banyan VINES, Microsoft Lan Manager, OS/2 LAN Server, and Windows NT networking. In practice, network operating systems provide file I/O redirection and file sharing services. File I/O redirection simply means that an application program need not be concerned with whether files are stored on a local drive or a file server over a network.

One of the most important things about cc:Mail is that the software components comprising the cc:Mail system are application software. In other words the basic cc:Mail technology is not a client/server system (although server processes can run atop the cc:Mail database). Technically, the user mail applications are not data communications
applications at all but database applications. Although client/server systems are very popular (including the servers that come with cc:Mail R8), the cc:Mail file sharing system has a number of strengths.

Network operating system and protocol independence: A cc:Mail system can be implemented in any network environment that supports file sharing and record locking. The software components comprising the cc:Mail system use standard file access mechanisms provided by the operating systems of the workstations on which they run. Redirection of file access mechanisms over a network is handled by the network operating system.

Distributed processing: No processing must occur on the file server. The cc:Mail user mail applications, administrative utilities, Routers and gateways all use the processing power of the workstations they run on. User mail applications communicate with each other by reading and writing data to post offices. Normally, no cc:Mail software runs on
the file server.

Interoperability: Interoperability is a function of the network operating system software and of applications. User mail applications running on different types of computers can access the same cc:Mail post office when the network operating systems supports file sharing across platforms. Most network operating systems support more than one
type of computer.

Platform-independent file attachment handling: Any file can be attached to a cc:Mail message and routed through a cc:Mail system. Files can be singular text or binary objects or they may be complex, consisting of multiple parts. Any user mail application can attach files. The integrity of complex files, such as Macintosh files, is preserved throughout the cc:Mail system, even when messages including these files are forwarded by user mail applications running in operating environments that do not support complex files.

Dedicated cc:Mail Routers and gateways: cc:Mail Routers and e-mail gateways run on dedicated workstations. In some network environments, however, Routers and gateways may also be run on a non-dedicated file server.

Is This Confusing?

One reason cc:Mail administrators and network professionals can sometimes find cc:Mail confusing is that not all of the cc:Mail system components work through file sharing. The cc:Mail Router, for example, is both a database application that moves messages between post offices and a powerful data communications program. The cc:Mail Router can communicate in a variety of ways with other cc:Mail Routers and cc:Mail Mobile users. Unlike user mail applications that access post office files independent of the lower layers of the network, the cc:Mail Routers and e-mail gateways sometimes use lower-level protocols to communicate with other software processes across a network.

Architectural Characteristics of cc:Mail

Other properties of the cc:Mail system stem from its underlying database technology, i.e., by its application-layer interface with the network operating system, including:

Cross-platform architecture: Since interoperability is built-in to all cc:Mail software components, the cc:Mail system is inherently cross-platform. The cc:Mail software supports several workstation operating systems. For the cc:Mail system to function across platforms, the network operating system must support the sharing of files between the different types of computers.

Data transparency: In a cc:Mail system messages can be exchanged between different types of computers without the need for data conversion. The cc:Mail database provides a common format for message data exchanged between different types of computers. As a result, cc:Mail messages produced on one type of computer can be read on another.

Instant local delivery: Message delivery is instant between users on the same cc:Mail post office. When cc:Mail a message is sent between users on the same post office, the mail application on the sender's workstation immediately writes the message into the recipient's mailbox. Sending and delivering the message are the same thing.

Store-and-forward: Messages that are addressed to users at other post offices or users of other e-mail systems are queued up for a cc:Mail Router or for an e-mail gateway. Messages are stored in the originating post office until a cc:Mail Router or e-mail gateway sends then to the next destination.

Efficient storage: When a message is sent to multiple recipients, only one copy of the message is stored in each post office. Only if a user replies to or forwards a message will a new copy be generated.

Why Does This Matter?

Many performance and reliability problems are related to where on the network cc:Mail system components are deployed and to the fact that the basic technology requires file access over a LAN. Understanding the relationship of a cc:Mail system to the network can help to avoid these problems and to trouble-shoot them when the occur.