When your server receives the ETRN command, it tries to send out all messages collected for the host specified as the ETRN command parameter. This method allows a dial-up system to get its messages immediately, instead of waiting for your server to make the next attempt to deliver the collected messages.
The SMTP module supports the ETRN command, so CommuniGate Pro can be used as a back-up mail server. No special setting is required, since this feature is always enabled.
The SMTP module uses the Router to process the ETRN parameter (domain name). It adds the wakeup fictitious user name to that domain to get a regular E-mail address wakeup@etrn-parameter and runs it through the Router. If the address is routed to an SMTP host, the SMTP module releases (wakes up) that host queue.
If you have routed the domain client.com to mail.client.com in your Router Table, all mail to the client.com domain will be kept in the mail.client.com queue. Since the ETRN command parameter is processed with the Router, too, the ETRN client.com command will correctly release the mail.client.com queue.
In a Dynamic Cluster environment, the ETRN command received by any cluster member releases domain queues on all cluster members.