MX records

Mark_Andrews at isc.org Mark_Andrews at isc.org
Mon Dec 9 22:47:53 UTC 2002


> We get mail addressed to:
> 
> user at calarts.edu
> user at muse.calarts.edu
> user at indy1.calarts.edu
> 
> and it should all go to muse.calarts.edu.
> 
> If muse is the mailhost, why does it need an MX record ? 

	Need no.  Should have yes.  The deliver of mail requires
	that a MX record be looked up.  If and only if there is not
	MX record will a A/AAAA records be looked up.  These
	subsequent lookup are to handle the transition from non-MX
	based deliver to MX based deliver.

	Having a MX record allows the answer to be cached MUCH
	longer than the negative answer which leads to less network
	traffic for DNS queries.  There are still a significant
	number of nameservers that don't cache negative answers.

	Also you will find that management is easier if you treat each
	address capable of receiving email the same.

	Mark

> At 10:38 AM 12/9/02 -0700, Cricket Liu wrote:
> >
> >Karyn Williams wrote:
> >> All mail send to this domain should go to muse.calarts.edu. From what
> >> I have read MX records are only for mail addressed to one host/domain
> >> to be forwarded to another. Is there any reason to have the MX record
> >> pointing to the addressed host (1) ?
> >> 
> >> calarts.edu.    IN      A       198.182.157.5
> >>                 IN      MX 0    muse
> >> ;
> >> ;
> >> ;
> >> ; IP block 198.182.157.0 through 198.182.157.255
> >> ;
> >> www.calarts.edu. IN     CNAME   muse
> >> indy1           IN      MX 0    muse
> >> muse            IN      A       198.182.157.5
> >>                 IN      MX 0    muse             <---------------(1)
> >
> >Only if you expect, or want to allow, people to address mail
> >to <user>@muse.calarts.edu.
> >
> >cricket
> >
> >Men & Mice
> >DNS Software, Training and Consulting
> >www.menandmice.com
> >
> >The DNS and BIND Cookbook, now available!
> >http://www.oreilly.com/catalog/dnsbindckbk/
> >
> >
> >
> -- 
> 
> Karyn Williams, CNE
> Network Services Manager
> California Institute of the Arts
> karyn at calarts.edu
> http://www.calarts.edu/network
> 
--
Mark Andrews, Internet Software Consortium
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark.Andrews at isc.org


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