Exchange 5.x will deque messages waiting for your domain over a dial-up connection.

To deque messages over a routed connection, you can schedule a batch file:

<b>@echo off
REM Cause dialup router to connect
ping <ip_address_of_ISP>
ping <ip_address_of_ISP>
if not %ERRORLEVEL% EQU 0 exit
REM If IMS not started, start it.
net start MSExchangeIMC
REM use 3rd party retrieval program or
REM FINGER your.domain.com@ISP.Host.domainisp.com or
REM use the AlwaysUseETRN registry value
REM stop IMS, if you started it.
net stop MSExchangeIMC
exit</b>
If using a single host (multiple hosts are very slow), you can use Regedt32 to navigate to:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIMC\Parameters

On the Edit menu, Add Value name AlwaysUseETRN, a type REG_DWORD value, and set the data to 1.

This will cause IMS to send an ETRN command to all ESMTP hosts it connects to, if they advertise support for ETRN, and are listed in the routing table as configured for IMS.