Question about MX records

John vo at eudoramail.com
Tue Mar 9 11:51:32 UTC 2004


Barry Margolin <barmar at alum.mit.edu> wrote in message news:<c2io9c$1mm0$1 at sf1.isc.org>...
> In article <c2idv8$otu$1 at sf1.isc.org>, vo at eudoramail.com (John) wrote:
> 
> > Hi all:
> > 
> > I have two mail servers:
> > 
> > IN    MX   10   server1 preferred.
> > IN    MX   20   server2 second choice.
> > 
> > My questions are:
> > 
> > 1. What is considered failure? if server1 has a problem
> >    and gives the incoming connection "connection refused"
> >    message? will the sending mail server jump to server2
> >    then? how does the dynamic work?
> 
> Yes, a failed connection attempt -- either a timeout while trying to 
> connect or a connection refused -- is the only thing that will cause 
> most mailservers to fail over to a backup MX.  I think RFC 2821 
> recommends also failing over due to certain types of errors encountered 
> after connecting successfully, but I don't know if many mailers have 
> been updated to conform to this.
> 
> > 2. If the DNS server that the incoming mailserver uses
> >    had cached the info including the old server1 info,
> >    will the mail server then keep trying it even though
> >    it's down?
> 
> It will keep trying them in order -- first server1, then server2.
> 
> BTW, do you have a question about the BIND nameserver?  It seems like 
> your questions are about mailservers, and would be more appropriate in a 
> mail-related newsgroup.

This is a question about MX records and how they work.
Thanks for the answer.


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