Re: [nznog] Continued problems with xtra email

On 9/1/07, 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?

...

Joe

Hamish. --

Well B and A might be branch mail servers for a company and C is another company trying to mail them. Normally B and A have their own Internet connection but one of them goes down. C can still send to the other one and then the mail can get through to the other one as they have their own private company network as well as the public Internet. Ian -- Web1: http://wand.net.nz/~iam4/ Web2: http://www.jandi.co.nz Blog: http://iansblog.jandi.co.nz