Re: [nznog] Continued problems with xtra email

On Sep 01, 2007 20:35:23, Hamish MacEwan wrote:

On 8/31/07, Joe Abley wrote:

...

[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.

I'm just curious what reasons, and they may be myriad, explain why SMTP will route around the damage using the MX priority, but TCP/IP won't? Ie, I can send mail where I can't send a packet?

Ah, I believe Joe was talking about the case where the MX servers are *different* servers, rather than the case (as with Xtra) where the same server is specified in multiple MX records. Jasper