Exchange - SMTP
- Dial-on-Demand Router Issues -

If you have a dial-on-demand router (ISDN for example) that connects to your ISP, the Dial-Up Connections feature of Exchange will not be useful to you. Exchange 5.5 has added an option based on ETRN to help here.  With previous versions of Exchange, you must go back to an old (Pre-4.0SP2) method of connecting and dequeuing the mail.

First, we will provide a couple of solutions that are based on the assumptions that you always want outbound mail delivered immediately, that you want to guarantee that queued inbound mail is delivered every X minutes, and that your ISP's mail host supports the ETRN protocol.  If you want to limit the schedule of outbound mail too, we would suggest you get an ISDN device that acts like a modem (a DigiBoard, Eicon, USRobotics, etc.).  If you must use an external device in this manner, the solution is ugly - but it is included here too.

Exchange 5.5

Exchange 5.5 has added a new registry key to force the IMS to send an ETRN whenever it connects to deliver outbound mail.  The one requirement here is that you use the "Forward all mail to:" option for your outbound mail.  This will be the server to which Exchange sends the ETRN to trigger the mail delivery.

The key is a DWORD with possible values of 0 and 1 (off - don't send, and on - send, respectively).

(HKLM\SYSTEM\CurrentControlSet\Services
\MSExchangeIMC\Parameters\AlwaysUseETRN)

This will cause mail to be dequeued from the ISP every time outbound mail is sent from your system.  This may be less regular than is acceptable for your inbound mail requirements, so you may need to force the issue.  You can schedule the delivery of a dummy mail message at the frequency you desire.  One alternative is to use a Link Monitor to generate the test message.  Another alternative is to use AT, WINAT (reskit), CROND (shareware), or another scheduling package to run a command line utility to send the mail message.  Our recommendation is a freeware tool called blat, but there are several choices available.

You can use the new exchsrvr\imcdata\pickup directory as an alternative to blat for sending mail.  Create a RFC 822 compliant message and place it in that directory (you can just copy a file there in fact) and it will get sent.  Here's a sample:

Finally, the AlwaysUseETRN directive always sends the command in the form "ETRN @domain.com".  In some cases the ISP either wants you to delete the "@" sign or use a "#" sign.  You will not be able to do this with AlwaysUseETRN.  You can still use dequeue.exe in the Custom Command field.

Pre-Exchange 5.5

In Exchange 5.0 and earlier, the only way to send an ETRN to your ISP's mail host is with an external program like dequeue.exe. You will need to schedule the program with AT, WINAT (reskit), CROND (shareware), or another scheduling package.

This method will also work with any version of Exchange server in the case where your ISP does not support ETRN, but the other two assumptions are true.  You can schedule the appropriate dequeueing command with the same tools.

The ugly solution

If you do not have POP or IMAP clients, this is also an option.  If you want to control the outbound delivery of mail in addition to triggering the dequeuing of inbound mail, this method will do it.  Outbound mail will remain in the MTA-OUT queue until the IMC/IMS is started (be careful of message timeouts here).

Create a batch file that has the following steps (syntax may vary on your system):

1. net start msexchimc
2. ping x.x.x.x (the ISP mail host - this should initiate the connection)
3. dequeue (either run dequeue.exe or one of the other commands to dequeue the mail)
4. sleep xx (wait a bit for the mail to deliver)
5. net stop msexchimc

This batch file will need to be scheduled with AT, WINAT (reskit), CROND (shareware), or another scheduling package.  Remember, there are some limitations here: you cannot use POP or IMAP clients with your Exchange Server using this method since they rely on the IMS to send mail.  The ugly part is that stopping and starting the IMC/IMS goes against the design of NT services and may result in severely delayed mail.