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.
To open the MTA Site Configuration properties sheet, follow these steps:
FIG. 14.1 The MTA Site Configuration is located in the Configuration container.
At this point, you have three property pages to configure:
To configure the General features, such as the display name of the MTA Site Configuration Object, follow these steps:
FIG. 14.2 The General page of the MTA Site Configuration properties sheet.
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.
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.
To set the messaging default values for the MTA Site Configuration object, follow these steps:
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.
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.
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:
FIG. 14.4 The Message Transfer Agent directory object is located inside the server container.
The following three pages become available for you to configure:
These pages are covered in the sections that follow.
To set values for the local MTA name and password and other general message transfer preferences for this server, follow these steps:
FIG. 14.5 The General page of the Message Transfer Agent properties sheet.
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
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.
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.
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.
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 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:
NOTE: The Internet Mail Connector and Microsoft Mail connector have separate queues that you can access through their properties sheets.
FIG. 14.6 Messages waiting to be delivered are held in the queue.
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.
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.