Frank Cox wrote: > On Thu, 01 Nov 2007 10:54:56 +0800 > Ed Greshko <[email protected]> wrote: > >> It is call "fault tolerance". In general, sending to a single IP address is >> has a single point of failure. If that system is down...email doesn't move. > > I realize that you can have many mailservers cascading in order of availability > by specifying multiple IP addresses in your MX records. However, a lot of > mailservers have only one IP address specified in their MX record with no > failover listed. It's part of the relevant RFP that the sending system is > supposed to retry on a failure anyway, so if the system comes back up within X > number of days the message is still delivered. > >> Sending to IP addresses doesn't scale and isn't manageable. > > Obviously, it doesn't scale that way, but still -- it's legal to have a single > IP address specified in your MX record and that comes to the same thing, pretty > much. > > I still don't see the difference. Well, for one, what happens if the server in question has a dynamic IP address and when it changes the system updates its DNS records to reflect the change. I did that years ago when I only had dynamic IPs for my domain. But I was still able to run a mailserver. If you relied on IPs it wouldn't work.