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Using Microsoft Exchange Server With a Dial-Up Internet Connection

The Internet Mail Connector in Microsoft® Exchange Server 4.0 provides a complete SMTP messaging solution for organizations that have dedicated Internet connections. However, the costs of dedicated Internet access vary in different regions around the world, and may be too high for some organizations to justify when all they require is e-mail connectivity. A less expensive alternative is to use a dial-up connection to an Internet service provider.

This document provides answers to common questions about how to use Microsoft Exchange Server 4.0 with a dial-up Internet Connection.

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Technical Information

Does the Internet Mail Connector Support uucp?

No, uucp is not supported in Microsoft Exchange Server 4.0. However, many service providers offer SMTP dial-up solutions that can be used with the Internet Mail Connector.

What kind of connection do I need to get from my service provider?

The Internet Mail Connector needs to be able to establish a TCP connection to your service provider's SMTP host. Therefore, any connection that supports TCP/IP services can be used, such as PPP or SLIP over phone lines or ISDN. When selecting the kind of connection that will be used you should consider the amount of Internet e-mail traffic you anticipate having, and make sure the bandwidth of the connection will be able to support it.

What must my service provider do to support a dial-up SMTP connection?

Your service provider must configure their SMTP host to act as a relay host for your domain. That means they must configure a DNS MX record that instructs all hosts to connect to their server to send mail to your domain. Their host must be configured to hold mail for your domain until your system dials in to retrieve it. Typically, your system will have to issue a command to their server when it connects to trigger it to deliver any mail it has queued.

How do I trigger my service provider's SMTP host to deliver my mail?

This will depend on your service provider. If they are using sendmail, there is a command option to force sendmail to process all queued items for a recipient address. You can use rsh to remotely execute this on the service provider's server:

rsh host "/usr/lib/sendmail"

Some service providers use other mechanisms to trigger mail delivery, such as issuing a finger command to a certain address. Ask your service provider for specific instructions on how to trigger mail delivery.

How do I configure my system to dial in to the service provider?

To use the Internet Mail Connector with a dial-up connection, create a batch file that initiates the connection and runs the Internet Mail Connector service to transfer mail. You can use the Microsoft Windows NT® schedule service to execute this batch file at specified intervals. See the Windows NT Online Help for information on using the schedule service.

The batch file must perform the following operations:

  1. Initiate the PPP/SLIP connection to your service provider. If you are using a dial-on-demand router, this step is not necessary.
  2. Start the Internet Mail Connector service.
  3. Trigger the service provider's SMTP host to deliver queued mail.
  4. Wait several minutes to allow inbound and outbound delivery to complete. The amount of time to wait depends on the maximum message size you want to allow.
  5. Stop the Internet Mail Connector service.
  6. Terminate the PPP/SLIP connection.

The Windows NT rasdial command can be used to initiate and terminate the connection. Below is an example of a batch file that manages a dial-up connection:

rasdial "My Provider" userid password

if errorlevel 1 goto callfail

net start "Microsoft Exchange Internet Mail Connector"

if errorlevel 1 goto startfail

rsh host "/usr/lib/sendmail"

sleep 600

net stop "Microsoft Exchange Internet Mail Connector"


rasdial "My Provider" /d


What if it takes longer to deliver a message than my connection allows?

When the Internet Mail Connector is stopped, it allows up to 60 seconds for any pending message deliveries to complete before shutting down. Any messages that are not delivered within 60 seconds will be retried at the next connection. Dial-up connections are of a fixed duration, so a message that takes longer than that amount of time to transfer will never be delivered - the sending host would keep retrying delivery until it eventually was returned as undeliverable.

With a dial-up connection you should consider setting a message size limit at the Internet Mail Connector. You should choose the message size limit and connection duration such that a message within the size limit can be delivered during a single connection. The size limit will prevent the Internet Mail Connector from trying to deliver inbound or outbound messages larger than the specified size. Users in your site will be prevented from sending large outgoing messages, but this will not protect against large incoming messages, since they must be transmitted over the connection before the Internet Mail Connector can reject them. Check with your service provider to find out if they can limit the sizes of messages they attempt to deliver to your domain.

How do I make sure the Internet Mail Connector doesn't time-out when sending messages over my low-bandwidth dial-up connection?

There are several registry values under the Internet Mail Connector Parameters key (HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeIMC\Parameters) that control time-outs:

SMTPRecvTimeout   -  waiting for packet transmission

SMTPWaitForAck    - waiting for OK response to a command
sent to another host

SMTPWaitForBanner  -  waiting for HELO banner from
another SMTP host

SMTPWaitForDataBlock  - waiting for the termination
to a DATA block

SMTPWaitForDataInitiation -  waiting for the start
of transfer of a data block

SMTPWaitForDataTermination - waiting for a response
to the termination of a data block

SMTPWaitForMailFrom -   waiting for a response to
the FROM command

SMTPWaitForRcpt  -   waiting for a response to the
RCPT command

These time-outs are specified in seconds. If a time-out occurs, an event will be written to the Windows NT event log. If these time-outs occur frequently, you may want to increase them. In particular, the default setting for SMTPWaitForDataBlock limits the data transfer for a message to 10 minutes. Over a low bandwidth line you may want to increase this value to allow more time for large messages to transmit.

What can I do to optimize the Internet Mail Connector's performance over a low-bandwidth connection?

Using the Microsoft Exchange Server Administrator application, open the Internet Mail Connector properties in the Connections container. The Advanced Transfer Mode options on the Connections page include settings for the maximum number of inbound and outbound connections, and for the maximum number of messages sent in a connection. The default settings are optimized for connections at LAN speeds. For a dial-up connection, you should set the maximum number of inbound and outbound connections to one each. You should increase the maximum number of messages sent in a single connection to a higher value, such as 50.

Performance over a low-bandwidth connection will also be improved if you configure the Internet Mail Connector to forward all mail to your service provider's SMTP host, and let it perform the DNS resolutions to deliver mail to the appropriate destinations.

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