mx priority question

Brian Keefer chort at smtps.net
Fri Jul 25 18:30:37 UTC 2008


On Jul 25, 2008, at 7:35 AM, birch69x at gmail.com wrote:

> Here is the setup:
> mx1.xxxx.com priority 10
> mx2.xxxx.com priority 20
>
> As I understand it, sendmail will try to use mx2.xxxx.com if
> mx1.xxxx.com is down? Well, but sendmail just put the mail in queue
> and tried mx1.xxxx.com later.
> Have I misunderstood the mechanism or what have I done wrong?
> Thanks.
>

If the first server answers, but returns an error during the SMTP  
session, most sending MTAs will treat that as a failed delivery  
attempt and queue the message to try later.

If the first server sends a TCP RST or the connection times-out, most  
MTAs will try the next listed MX record.  It's nothing to do with  
DNS, it's just MTA behavior.



Brian Keefer
Sr. Systems Engineer
www.Proofpoint.com
"Defend email.  Protect data."



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