Re: [nznog] Continued problems with xtra email

On 29-Aug-2007, at 0431, Blair Harrison wrote:

On 8/29/07, Don Stokes wrote:

...

I've always advised that if a secondary MX host isn't going to do anything useful with incoming mail other than re-queue it for delivery, then just don't bother.

I'd have to wholeheartedly agree with that.

[A] --------- [B] \ / X / X / \ / [C] [A], [B] and [C] are different networks on the Internet. I have a priority-0 MX installed at [A], and another one at [B]. The MX at [A] has a lower number in its RDATA than the one at [B] (i.e. the one at [B] is the backup). Suppose some device at [C] tries to send me mail, and at the time it chooses to attempt delivery, there's a network problem which prevents traffic from getting through. It instead delivers to the backup MX at [B]. There is no network problem between [B] and [A], so mail is forwarded on straight away. With this configuration, mail from the host at [C] can be delivered to the ultimate destination mailbox in near real-time. Without a backup MX at [B], the mail would be queued at the server at [C] and re-submitted at some later time, meaning that the mail will be delayed for as long as it takes to fix the path between [C] and [A], and then some. I have this kind of setup in place for my various non-employer e-mail accounts, and I see the backup MX being exercised all the time. This suggests that using a backup MX is a win, for me. Joe