I’m confronted with the task of changing the flow of email for a group of people in a European country. Currently mail is delivered to a local provider, and users connect to that and retrieve messages via POP3 (Post Office Protocol). With a minimum of downtime, the domain to which messages are currently addressed will be hosted on a different network, and email will be routed over internal communications lines to a new server at that location. First things first: acquire control over the DNS entries. I’ve done that already, and have set the time to live (TTL) for each of the MX records to 120 seconds, allowing me to make a modification and have that propagated in about two minutes. Recall that the MX entries of the Domain Name System indicate which hosts mail should be delivered to. I’m then going to set up our venerable Exim mail servers to do the internal routing. I can prepare most of that, as in effect it is merely a matter of adding an entry to the manualroute router. As soon as the target server is up and running, users have been created and the POP3 clients have been tested, I will have the internal destination of the manualroute‘d host point to an impossible IP address, and I’ll change the public DNS to point the MX records at our hosts. Mail will queue up of course, unable to be delivered, and as soon as everything works smoothly, I change the manualrouted host to have it deliver to its final destination. I’ve done this before, but this time I’m on a specially tight schedule. ;-)

Mail, Exim, and Linux :: 13 Feb 2007 :: e-mail