Messaging Server

A messaging server is any server on the network that hosts one or more Novell NetMail agents. In eDirectory^TM, the messaging server is represented as a Container object with server attributes: it defines the messaging server properties and it contains all NetMail agents running on that server.

Creating the Messaging Server

NetMail 3.5 gives administrators the option of creating the Messaging Server object during installation or creating it after installation using WebAdmin. For ease of use, it might seem logical to simply create the Messaging Server object during installation; however, doing so assumes that you want to create the messaging server in the Internet Services container, that you want the server to function in distributed mode, and that you want to run the NMAP Agent on the server.

These are large assumptions that impact the functionality of your overall messaging system. Therefore, before deciding whether to create the Messaging Server object during or after installation, you need to consider the preceding issues of whether the messaging server is going to function in distributed or standalone mode, where you want to create the Messaging Server object, and what agents you want to run on the server.

The following sections discuss these issues and review how to create the Messaging Server object during or after installation:

• Distributed or Standalone?
• Where Should the Messaging Server Object Be Located?
• What Agents Do I Want to Run on the Messaging Server?
• Creating the Messaging Server During Installation
• Creating the Messaging Server after Installation

Distributed or Standalone?

The first issue to consider before creating your Messaging Server object is whether the messaging server is going to run in distributed or standalone mode.

By default, messaging servers are created in distributed mode; that is, they look for other Messaging Server objects in the Internet Services container. This enables messaging system functions to be distributed over several servers.

Standalone messaging servers do not search the Directory tree for Internet Services and its associated messaging servers. Instead, they act as independent messaging systems, exclusively providing all NetMail services to the users within their assigned contexts.

To configure a standalone messaging server, you must disable Distributed Processing in the messaging server's configuration menu. This prevents the messaging server from looking for other Messaging Server objects in the Internet Services container.

For an overview of standalone and distributed messaging servers, see Messaging Server. For help in determining whether distributed or standalone messaging servers best suit your messaging system environment, see Selecting Your NetMail System Configuration.

Where Should the Messaging Server Object Be Located?

Associated with the question of whether the messaging server is going to run in distributed or standalone mode is the issue of where the Messaging Server object should be located.

Typically, messaging servers are created in the Internet Services container because most messaging systems function in distributed mode and distributed messaging servers look for other Messaging Server objects in the Internet Services container.

In some instances, however, messaging systems require standalone configurations. Messaging Server objects located outside the Internet Services container are not recognized by other messaging servers. Consequently, standalone messaging servers are usually created outside Internet Services.

It is important to remember, however, that creating a Messaging Server object outside the Internet Services container only prevents other messaging servers from interacting with the messaging server. All messaging servers, even those located outside the Internet Services container, search the Directory tree for other Messaging Server objects in Internet Services. Therefore, to define a standalone messaging server, you must disable Distributed Processing in the messaging server's configuration menu, even if it is created outside Internet Services.

Creating Distributed Messaging Servers Outside Internet Services

In some situations, you might want to create a Messaging Server object outside the Internet Services container and have it continue to function in distributed mode. For example, to easily delegate system administration, you can create Messaging Server objects in the same containers as the users they service and simply grant administrative rights on a container basis.

Messaging servers located outside the Internet Services container can continue to operate in distributed mode if you create Alias objects for them within Internet Services. Alias objects enable distributed messaging servers to locate and interact with messaging servers outside the Internet Services container in the same way they interact with messaging servers inside the Internet Services container.

NOTE:  You cannot create Alias objects in WebAdmin; therefore, you must use another administrative tool, such as iManager, to create the Alias object in the Internet Services container.

What Agents Do I Want to Run on the Messaging Server?

The final issue to consider before deciding whether to create the Messaging Server object during or after installation is which agents you want to run on the messaging server. This again, depends on whether the messaging server is going to run in distributed or standalone mode.

Agent Distribution in Distributed Environments

Distributed messaging systems can share agent services among multiple messaging servers. Therefore, in planning your distributed messaging system, you need to decide which agent services you want to provide to your users and how to distribute those agents.

In part, agent distribution depends on the server resources required for any given service and its volume of usage. For example, in messaging systems with a high volume of e-mail client usage, you might want to run the POP, IMAP, and Modular Web Agents on a dedicated, high-performance e-mail server. Or, in environments with heavy proxy usage, you can create a dedicated Proxy server and configure the Proxy Agent to query its user accounts every hour.

Another point to consider in agent distribution is fault tolerance. Identify your most critical services and distribute those agents accordingly. For example, you can run the SMTP Agent with an NMAP Agent on a dedicated server to insulate your messaging system from denial-of-service attacks. By not assigning any user contexts to the NMAP Agent, the NMAP Agent functions as a dedicated queue server, exclusively handling all incoming messages from the SMTP Agent. With this configuration, no users are impacted in the event of a spam attack and the messaging system's remaining NMAP Agents are free to continue processing and delivering internal messages. For more information on providing fault tolerance through agent distribution, see Building Fault Tolerance in NetMail.

Finally, in planning agent distribution, you must consider the message path. The message path is where a message goes from the time it enters the message system to the time it is delivered to a user's mailbox.

All messages enter the messaging system through the SMTP, Proxy, or Modular Web agents. These agents, in turn, queue incoming messages to a queue server. The NMAP Agent on the queue server places the messages in the message queue where they can be processed by NetMail queue agents. After messages are processed in the message queue, the NMAP Agent on the queue server delivers the messages to the NMAP Agents responsible for the recipients' mailboxes.

NOTE:  The AntiVirus, AntiSpam, List, Alias, AutoReply, Rule, Calendar, and SMTP agents are all queue agents. For a complete description of how messages are processed in the message queue, see Message Processing in the Message Queue. For an overview of each agent's function, see NetMail Agents. For a detailed explanation of each agent's configuration options, see NetMail Configuration.

When you create and configure NetMail Agents in a distributed messaging system, you must ensure that the message path is linear---that is, each queue agent should only process the message one time as it goes from the queue server to the message store.

In a distributed messaging system with one NMAP Agent, there is only one queue server and one message store. They are both managed by the same NMAP Agent. Consequently, the message path is always linear.

However, in distributed messaging systems with multiple NMAP Agents, there can be multiple queue servers and multiple message stores. It is, therefore, possible for a message to be processed twice by the same agents on its way from the queue server to the message store.

For example, in the preceding diagram, Server A is the queue server for the SMTP Agent and Server B is the queue server for the Proxy Agent. Both queue servers are monitored by the AntiSpam and AutoReply agents. Server B also hosts the message store.

In this scenario, the message path for a message entering the message system through the Proxy Agent is as follows:

1. The Proxy Agent queues the message to Server B.
2. The NMAP Agent on Server B puts the message in the message queue where it is processed by the AntiSpam and AutoReply agents.
3. The NMAP Agent on Server B then delivers the message to the recipient's mailbox.

This message path is linear; that is each queue agent only processes the message one time as it goes from the queue server to the message store.

However, when a message enters the message system through the SMTP Agent, the message path is as follows:

1. The SMTP Agent queues the message to Server A.
2. The NMAP Agent on Server A puts the message in the message queue where it is processed by the AntiSpam and AutoReply agents.
3. The NMAP Agent on Server A hands the message off to the NMAP Agent on Server B so it can be delivered to the recipient's mailbox.
4. The NMAP Agent on Server B puts the message in its own message queue where it is reprocessed by the AntiSpam and AutoReply Agents.
5. The NMAP Agent on Server B then delivers the message to the recipient's mailbox.

This message path is redundant; that is, messages are processed twice by the same agents. Reprocessing messages wastes your system resources and duplicates agent actions. In this sample scenario, autoreply messages are sent twice for every message and forwarded messages are sent twice if the recipient configured message forwarding to keep a local copy of the message. Messages are also scanned twice for viruses. Depending on messaging traffic, this can place a significant load on the virus scanning engine and create a bottleneck in the message queue, slowing overall system performance.

To avoid reprocessing messages in distributed messaging systems with multiple NMAP Agents, you can do one of the following:

• Manage queue server and message store functions on different NMAP servers. This means that the NMAP Agents on queue servers (that is, the servers to which the SMTP, Proxy, and Modular Web agents queue messages) do not have any users in their assigned contexts.

  NOTE:  All NMAP Agents with users in their assigned contexts have a message store. For more information on the NMAP Agent's Context property, see Configuring the NMAP Agent

  You must then configure the queue agents (the AntiVirus, AntiSpam, List, Alias, AutoReply, Rule, Calendar, and SMTP agents) to monitor all the queue servers or all the message stores, but not both. This ensures that no agent is processing messages at both ends of the message path.

  Ideally, we recommend that all queue agents only monitor queue servers and that no queue agents, other than the SMTP Agent, monitor the message store.

  NOTE:  You must configure an SMTP Agent to monitor the message store because the NMAP Agents responsible for the message store can generate bounced messages and quota return messages.

• If you cannot have dedicated queue servers and dedicated messages stores, configure the SMTP, Proxy, and Modular Web agents to queue to the same queue server. You must then configure the queue agents to monitor only that queue server. This is the only way you can avoid reprocessing yet still ensure the queue agents process every message.

Agent Distribution in Standalone Environments

Because standalone messaging servers function independently of each other, they must have all the NetMail agents required for a self-contained messaging system.

At a minimum, each messaging server must have the following agents:

• NMAP
• SMTP
• A client agent (POP, IMAP, or the Modular Web Agents)

Additional agents depend on the services you want to provide to your users.

The NMAP, SMTP, POP, IMAP, Modular Web Agent, AutoReply, Rule, Proxy, Alias, AntiSpam, AntiVirus, List, and Connection Manager agents must run locally on standalone messaging servers.

If you run the Address Book Agent on a standalone messaging server, it returns only local users in address book queries. To provide a system-wide address book, you can run the Address Book Agent on a distributed messaging server and configure the local e-mail clients to access the distributed Address Book Agent as an LDAP server.

For an overview of each agent's function, see NetMail Agents. For a detailed explanation of each agent's configuration options, see NetMail Configuration.

Creating the Messaging Server During Installation

Creating the messaging server during installation automatically creates a distributed Messaging Server object with an NMAP Agent in the Internet Services container. If these conditions do not meet your criteria, you must create the object after installation using WebAdmin.

When you select the Configure Messaging Server option during installation, the installation program prompts you for the following information:

The installation program automatically creates a Messaging Server object with an NMAP Agent in the Internet Services container.

Creating the Messaging Server after Installation

After installing NetMail 3.5, you can create Messaging Server objects using WebAdmin. To create the messaging server object, select the container in which you want to create the messaging server and choose Messaging Server from the Create menu.

In creating the Messaging Server object, you are prompted for the following information:

Configuring the Messaging Server

From the Messaging Server's configuration menu, you can configure the following options: