Question about MX records

[Barry Margolin]

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.

-- 
Barry Margolin, barmar at alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***