Special Edition Microsoft Exchange Server 5.5

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Message Transfer Configuration



The Microsoft Exchange Message Transfer Agent (MTA) is the key component that provides addressing, routing, and message delivery. Proper configuration of MTA settings is important to an efficient Exchange organization. As described in Chapter 3, "Exchange's Integrated Server Components," a message that originates in an Exchange mailbox reaches its destination in only two ways. The first is when a message is addressed to a user on the same Exchange server and is delivered by the information store. The second is when a message is addressed to a user on a different server or foreign system, and the MTA handles the message transfer.

Understanding the Transfer Agent Components

The Microsoft Exchange Message Transfer Agent is a Windows NT service running on each Exchange server in your organization. For connection to Microsoft Mail systems, an additional service called the Microsoft Mail Connector (PC) MTA negotiates message transfer with Microsoft Mail networks.

Configuration of the Exchange MTA is handled through two sets of properties sheets:

Some of the essential parameters involved in performing MTA site configurations are listed here:

Message Tracking. To keep records of Message Transfer Agent activity within a Microsoft Exchange site and enable message tracking. A daily log file is generated and stored in the EXCHSRVR\TRACKING.LOG directory. Message tracking log files are in a text format. The full file name, to use an example, might be EXCHSRVR\ TRACKING\970122.LOG. The individual log files are named using this format: YYMMDD.log. For example, a log file for MTA activity on Jan 22, 1997 would have the name 970122.log.

Message Queues. Each server has a list of messages that are waiting to be delivered by its MTA. The queues are distinguished as being either Private or Public information store messages. Messages are held in the queue until the MTA can successfully transfer the messages by establishing a connection with the remote MTA or until the messages exceed their lifetimes (as set in the messaging defaults).

Messaging Defaults. Settings for how (and how long) to transfer a message before certain timeouts occurs are called messaging defaults. These values are set in the MTA Site Configuration properties and are used by all MTAs in the site unless a specific connection uses MTA override parameters.

MTA Overrides. Certain connectors (specifically, the dynamic RAS connector and the X.400 connector) provide for object-specific MTA settings. Use the Override property to change the default Microsoft Exchange Server MTA attributes when using a specific X.400 or dynamic RAS connector. Remember their existence when you define messaging defaults in the MTA Site Configuration properties sheet. The Override property is for developing flexibility in MTA configuration.

Performing MTA Site Configuration

To open the MTA Site Configuration properties sheet, follow these steps:

1. Navigate to your desired site with the Exchange Administrator program, and then expand the site container.

2. Highlight the Configuration container of the selected site (see Figure 14.1). All the site configuration objects appear in the right pane of the Administrator program's window.

FIG. 14.1 The MTA Site Configuration is located in the Configuration container.

3. Select the MTA Site Configuration object from the list.

4. Open the MTA Site Configuration Object properties sheet by double-clicking the object.

At this point, you have three property pages to configure:

The General Tab

To configure the General features, such as the display name of the MTA Site Configuration Object, follow these steps:

1. Click the General tab of the MTA Site Configuration properties sheet (see Figure 14.2).

FIG. 14.2 The General page of the MTA Site Configuration properties sheet.

2. Type a new name in the Display Name box, if you want. The default name is MTA Site Configuration.


NOTE: By default, the directory name is Site-MTA-Config, and it cannot be changed. This is the unique object name that the site MTA has assigned.
3. Click the Enable Message Tracking check box to instruct the System Attendant to keep a daily log of all messages processed by the MTA. This check box corresponds to the "Enable Message Tracking" check box in the Information Store Site Configuration properties sheet. Both enable message tracking, but only for their respective services.

4. Click Apply to set these properties and continue viewing and changing other properties.

5. When you finish changing settings, click OK to return to the Administrator program.

The Permissions Tab

This page of the properties sheet allows you to define certain Windows NT user accounts that have rights to modify this directory object. See Chapter 12, "Using the Administrator Program," for a detailed description on working with the standard Permissions properties sheet.

The Messaging Defaults Tab

To set the messaging default values for the MTA Site Configuration object, follow these steps:

1. Click the Messaging Defaults tab of the MTA Site Configuration properties sheet (see Figure 14.3).


TIP: To return to the default Message Transfer Agent settings, click the Reset Default Values button.

FIG. 14.3 Messaging defaults control each connection made by the MTA.

2. Enter specific MTA configuration variables, as described in Table 14.1.

To the right of each item listed in the table is a box that contains a default numeric value. Replace any value with a number that will be used in establishing a connection through any MTA in the current site.

3. Click Apply to set these properties.

4. When you finish changing settings, click OK to return to the Administrator program.

Table 14.1  MTA Site Configuration Parameter Values

Variable Description
RTS Values Reliable Transfer Service (RTS) values determine how often you want to verify information as it is being transferred, how long you want to wait after an error to restart the transfer, and how often you want a verification that another system has received your transfer.
Checkpoint Size (K) Sets the amount of data to be transferred before a checkpoint is inserted. If an error occurs and the message must be retransferred, the process restarts from the most recent checkpoint. If you specify zero, no checkpoint is set. The default is 30. Checkpointing slightly reduces transmission speed. You should decrease the checkpoint size when the link is less reliable.
Recovery Timeout (Sec) The amount of time after an error occurs that the MTA waits for a reconnection before deleting checkpointed information and restarting the transfer from the beginning. The default is 60.
Window Size The number of checkpoints that can go unacknowledged before data transfer is suspended. The greater the window size, the greater the transfer rate. The window size determines the amount of resources set aside for the receiving station. Specify window size only if the checkpoint size is greater than zero. The default is 5.
Connection Retry Values Connection retry values determine how many times you want to try to open a connection and send a message and how long you want to wait to reopen a connection or resend a message after an error.
Max Open Retries The maximum number of times the system tries to open a connection before it sends a non-delivery report (NDR). The default is 144.
Max Transfer Retries The maximum number of times the system tries to transfer a message across an open connection. The default is 2.
Open Interval (Sec) The delay (in seconds) between attempts to open a communication channel. By default, the delay is 600 seconds.
Transfer Interval (Sec) The delay (in seconds) between attempts to retransmit a failed message packet. By default, this delay is 120 seconds.
Association Parameters Associations are paths that are opened to other systems. Each association is contained within a connection and is used to transfer messages to a system. You may have multiple associations in each connection. You can determine how long to keep an association, how long to wait for a response before disconnecting, and the number of messages you will let wait before you open another association.
Lifetime (Sec) The maximum time that an idle connection between MTAs remains open. By default, an idle link is held open for 300 seconds after the last communication.
Disconnect (Sec) The maximum time allowed for establishing or terminating a connection before the session is ended independently. By default, this time is 120 seconds.
Threshold (Msgs) The maximum number of queued messages to a remote system. When this is exceeded, the MTA opens another association. The default is 50.
Transfer Timeouts (Sec/K) Messages of different priorities require different levels of attention. For example, an urgent message is processed more quickly than a non-urgent message. If a transfer fails, you must determine how long to wait before sending a non-delivery report (NDR). The transfer timeout is the amount of time to wait before sending that NDR. You can assign a different amount of time for each message priority.
Urgent The delay (in seconds per kilobyte of total message size) between retries of urgent messages. By default, this delay is 1,000 seconds. This is a timeout value before messages are sent.
Normal The delay (in seconds per kilobyte of total message size) between retries of normal messages. By default, this delay is 2,000 seconds. The trend here is that the less important the message, the longer you wait for a transmission.
Non-Urgent The delay (in seconds per kilobyte of total message size) between retries of non-urgent messages. By default, this delay is 3,000 seconds.


NOTE: If you combine the default 144 Max Open Retries with the default 600-second Open Interval, Exchange waits 24 hours before returning a message as undeliverable.

The following section discusses configuring Message Transfer Agent properties for each Microsoft Exchange Server.

Configuring Local MTA Properties

Each Microsoft Exchange Server has a Message Transfer Agent. The MTA properties sheet is designed to configure and manage this service.

First, you must select the MTA from the server within your site. Follow these steps to do so:

1. Navigate to your desired site with the Exchange Administrator program, and then expand the site container.

2. Highlight the Configuration container of the selected site. All the site configuration objects appear in the right pane of the Administrator program's window.

3. Open the Servers container by double-clicking it. A list of Exchange servers in your site appears.

4. Click the name of the server that houses the MTA you want to configure (see Figure 14.4). A list of server objects appears in the right pane of the Microsoft Exchange Administrator program window.

FIG. 14.4 The Message Transfer Agent directory object is located inside the server container.

5. Click the Message Transfer Agent object, and then open its properties sheet.

The following three pages become available for you to configure:

These pages are covered in the sections that follow.

The General Tab

To set values for the local MTA name and password and other general message transfer preferences for this server, follow these steps:

1. Click the General tab of the Message Transfer Agent properties sheet (see Figure 14.5).

FIG. 14.5 The General page of the Message Transfer Agent properties sheet.

2. Type a name in the Local MTA Name box. This name will be used by remote MTAs (either on remote Exchange servers or foreign messaging systems) to identify this MTA. By default, this name is the name of the Exchange server on which the MTA is installed.

3. Type a password in the Local MTA Password box, if necessary. If you enter a password in this box, any remote MTA (either on remote Exchange servers or foreign messaging systems) must be configured to provide this password for authentication. By default, this box is blank, and no authentication is required of the remote MTA.


NOTE: If you decide to change the Local MTA Name or to add or change the Local MTA Password, be sure to take into consideration any previously established MTA connections. All remote sites (and foreign systems, such as X.400) must be adjusted to reflect the new information. Authentication is never required between two MTAs in the same site.  n
4. In the Message Size section, click the option button that indicates how you want to restrict the passage of messages through this message transfer agent.

Click the No Limit option button to allow this MTA to deliver messages of any size.

If you want to set a size limit, click the Maximum (K) option button, and then, in the text box, type an upper limit (in kilobytes) for messages that travel through this MTA. Any message that exceeds this size limit will be returned as undeliverable.


TIP: Use these settings as a filter to manage the messaging load for all traffic to and from this server. The upper-limit settings have precedence over message-size settings in individual connectors and recipient objects.
5. Click the Recalculate Routing button to rebuild the routing tables for this MTA. (See Chapter 2, "Understanding Exchange's Organization and Sites," for more information on routing tables.) New routing information for this MTA will propagate to all Exchange servers within the site automatically.


TIP: Rebuilding routing tables sometimes takes several minutes, so it is a good idea to go through each MTA properties sheet, make all changes, and then recalculate routing.


NOTE: Routing tables are rebuilt once a day automatically. The routing table will rebuild when it detects a change in a new gateway or a change in a connector configuration.
6. Click the Expand Remote Distribution Lists Locally check box to force distribution lists created on remote sites to be expanded on this server. When a message is sent to a distribution list by a user on this server, the message is split into its component recipients locally. If this box is not checked, the distribution list is expanded in the remote site, following the configuration in the distribution list's own properties sheet. By default, this box is checked, and distribution lists are expanded locally.


NOTE: Consider both the physical location of the majority of the distribution list's recipients and the messaging load on the local server. If you choose the default settings, make certain that the local server can handle the extra messaging traffic: Expanding large distribution lists can be a considerable load on an already overburdened Exchange server. Also, if you know that the majority of the distribution list's recipients reside on Exchange servers in the remote site, consider allowing the list to be expanded there.
7. Click the Convert Incoming Messages to MS Exchange Contents check box to convert all messages to Exchange's MAPI-compliant format automatically. By default, this option is not selected, and messages are kept in the format in which they arrive at the MTA (such as standard X.400 format).

8. Click the Only Use Least Cost Routes check box if you don't want this MTA to reroute messages destined for an unavailable server through another possible route. This option configures an individual message transfer agent (MTA) to send messages using only least-cost routes. Only the least-cost route for each message will be attempted. This allows you to prevent messages from being routed to connectors in other sites when a connector in the local site is unavailable. If a message cannot be routed through the least-cost route, Microsoft Exchange Server generates a non-delivery report (NDR).

9. If you want, make an entry in the Administrative Note text box.

10. Click Apply to set these properties and continue with other properties.

11. When you finish changing settings, click OK to return to the Administrator program.

This page controls the functioning of local server MTA. Using this page you can limit the message size sent, how messages are routed when multiple routes are available, and where distribution lists are expanded.

The Queues Tab

The Queues tab of the Message Transfer Agent properties sheet lists messages that are awaiting delivery by the MTA. The two primary windows are Queue Name (which shows the queue that you are currently viewing) and Message List (which displays the messages in that queue). From the Message List window, you can view details about a specific message in the queue, change a message's delivery priority, or delete it.

The Message List window has three columns that contain information about a particular message:

To configure the Queues property page, follow these steps:

1. Click the Queues tab from the Message Transfer Agent properties sheet (see Figure 14.6).

2. From the Queue Name drop-down list, select the message queue you want to display. The list shows queues for the private and public information stores, as well as for any installed gateways.


NOTE: The Internet Mail Connector and Microsoft Mail connector have separate queues that you can access through their properties sheets.
3. Select a message, and then click Details to view additional information about it. The additional message information includes the message originator, submit time, message size, and priority. This button is dimmed if no messages are in the queue.

FIG. 14.6 Messages waiting to be delivered are held in the queue.

4. Click the Refresh button to update the Message List window with the latest list of messages in the MTA queue.

5. Click Priority to display the message's priority, and then change the priority of the message if you want. Priority can be low, medium, or high. Messages are sent in order of priority. A message's priority is set when a message is created.

6. To remove a message from the MTA queue, select a message and click Delete.

7. Click Apply to set these properties and continue with other properties.

8. When you finish changing settings, click OK to return to the Administrator program.

Using this page, you can monitor the messaging queues on this server. You can monitor the dynamic RAS connector, X.400 connector, Internet Mail Service, and public and private information stores.

The Diagnostics Logging Tab

This properties sheet works in conjunction with the Windows NT Event Log to record various "events" that occur within the message transfer agent.

Various levels of logging determine what constitutes an event and, therefore, what types of information are actually recorded. For troubleshooting purposes, you would want a very detailed record of occurrences within the MTA; hence, you would set a high logging level. Normally, however, you want to log only critical events. So set a lower logging level for everyday operation.

FIG. 14.7 The Diagnostics Logging page for the site MTA.


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