DNS, MX Record

Mark.Andrews at nominum.com Mark.Andrews at nominum.com
Thu Sep 21 01:09:33 UTC 2000


> Hello All:
> The company that I work for has been having some problems receiving e-mail
> recently that has been perplexing me. I am hoping that someone may have some
> ideas as to a solution.
> 
> The company that I work for is hosting it's website at a virtual host
> provider (Webhosting.com), and the domain name is metzgers.com. We have an
> in-house Unix box (Cobalt Qube) that houses our mail (both Pop and SMTP). We
> are connected to the Internet by a NAT dedicated ISDN line that has 24/7
> connectivity. Static IP address is 206.165.56.209 and we have the A name
> media.metzgers.com registered to that IP address. Our router passes the
> request for POP and SMTP ports to the internal address of our Qube.
> 
> The problem that I am having is that mail is delayed from some servers by 24
> hours or more. Mail coming from other locations is instant. Some of the
> messages I am receiving (people are faxing the failure reports to me) are
> Host connect failed - destination host not responding, connection reset, and
> read error.

	This sounds like a buggy NAT or network link.  By the time MTA's get
	to this stage the DNS operations are way out of the picture.

> 
> Internal mail of course works fine and sending mail works fine. As I said,
> most mail seems to come through fine also, just not all of it. This is what
> stumps me. It is easier to diagnose something when it effects everything,
> but difficult when it effects part of the situation.
> 
> Here is my MX record, which is maintained by Webhosting.com:
> metzgers.com preference = 10, mail exchanger = media.metzgers.com
> metzgers.com preference = 0, mail exchanger = media.metzgers.com
> metzgers.com nameserver = ns1.dynamicweb.net
> metzgers.com nameserver = ns2.dynamicweb.net
> media.metzgers.com internet address = 206.165.56.209
> ns1.dynamicweb.net internet address = 205.178.159.134
> ns2.dynamicweb.net internet address = 205.178.138.137
> 
> We don't have a backup mail server as of yet, so is both preferences
> required that point to media.metzgers.com? (What is preference=0 used for?
> Webhosting.com tells me that it is the timeout value and is required,
> although as I do a lookup on other servers, it does not appear that many use
> it.) Could that be causing a loop that is delaying the delivery of mail?

	As you don't have a backup server you only need to list 1 MX
	record.  The preference field is so that other MTA's will pick
	your main mail server before trying your backup server when you have
	two.  Mail exchanges are tried in preference order lowest to highest.

	i.e. the main server has the lower numeric value.

	There is nothing magic about 10 or zero.  You could choose
	64000 and 64010 and have the same results. It's just a 16 bit
	numeric field for ordering the records.
	
> 
> Should our MX record read:
> metzgers.com preference = 10, mail exchanger = media.metzgers.com
> metzgers.com nameserver = ns1.dynamicweb.net
> metzgers.com nameserver = ns2.dynamicweb.net
> media.metzgers.com internet address = 206.165.56.209
> ns1.dynamicweb.net internet address = 205.178.159.134
> ns2.dynamicweb.net internet address = 205.178.138.137
> 
> Anyway, I am stumped and was hoping that someone would be able to shed some
> light into this issue. You know how people can become when they don't get
> their e-mail, and they are coming after me :-)
> 
> 
> Eric Leslie
> InfoSys/New Media
> Metzgers Printing & Prepress
> ________________________________
> E-mail: eric.leslie at metzgers.com
> Website: www.metzgers.com
> Phone: (419) 861-8611
> Fax: (419) 861-3299
--
Mark Andrews, Nominum Inc.
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark.Andrews at nominum.com



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