I would like to know is there anyone who know how to or a site with the how to on configuring a sendmail box to queue the mail only when the primary mail server is down. And when the primary mail server is up it will issue an ETRN command to the queue server to start processing and pushing the mail that is queued to the primary server. I am very much aware about the MX record priority on the DNS server but just need to configure the secondary mail server only. Thank you.