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Where should my two MX records point?

Posted on 2006-11-21
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Last Modified: 2008-02-01
We're hosting our own email on our Exchange server. A couple of days ago we signed up with godaddy for hosting a web site for us. Overnight our Mx records apparently got changed. When I log into our godaddy account I can edit our MX records. There are two MX records and I am not an MX record guru. Why are there two MX records and where should they point? I've got the first one, priority 0, pinting to our public IP address here our Exchange server is. Not sure what to do with the second one or if I've set the first one correctly. Thanks.
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Question by:WineGeek
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16 Comments
 
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olifarago earned 1000 total points
ID: 17989036
Hi WineGeek,

If you have your mail delivered directly to your exchange server (i.e. not being delivered through any third party spam/virus filtering organisation) then your primary MX should indeed point to the public IP address in your organisation over which SMTP traffic will be routed to your exchange server.

As for a second record, any other record with a lower priority will be used as a backup record and this is where mail will be delviered if your server is unreachable.  You could for example point this to another exchange server in your organisation (if you have multiple branch offices), or a third party provider of "store and forward" hosting whereby they will accept the mail on your behaldd if your server is unreachable and will continue trying to deliver it for you for an extended period of time.

If you have no such back in place, or no such backup requirement then you have no need for a second MX record.

Hope this helps,

Cheers!
Oli
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Author Comment

by:WineGeek
ID: 17989091
So MX records with higher priority numbers get looked at first or the other way around?
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Expert Comment

by:olifarago
ID: 17989125
The smaller the preference number, the higer the priority.

To clarify a record with a pref of 0 would be used before a record with a pref of 30.

Hope this is clear.

oli
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Assisted Solution

by:mikeleebrla
mikeleebrla earned 1000 total points
ID: 17989168
1.  MX records do NOT point to IP addresses.  MX records point to FQDNs (fully qualified domain names).  There will be an A record for that FQDN that in turn points to an IP address.

2.  >>So MX records with higher priority numbers get looked at first or the other way around?
a) it doesn't matter since you only have one exchange server i believe
b)MX=10
   MX=20

10 will be looked at first,,, if 10 is down, then 20 will be used.


http://www.intermedia.net/support/kb/default.asp?id=903
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Author Comment

by:WineGeek
ID: 17989185
godaddy is hosting out web site but we are hosting our mail. How does this affect the fact that your MX records point to your A records? Would I need multiple A records? Thanks
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Expert Comment

by:mikeleebrla
ID: 17989295
>>How does this affect the fact that your MX records point to your A records?
it doesn't affect it at all.

>>Would I need multiple A records?
one for each host of course

the A record for your mail.domain.com needs to point to your public address of your email server that you host internally
the A record for your www.domain.com needs to point to the address that godaddy assigned to you for your www site.

thats it.

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Expert Comment

by:olifarago
ID: 17989361
Indeed, apologies if my answer above was misleading, you should never point am MX record directly to an IP address, while it will work in the majority of cases, some mail servers will be unable to deliver mail to you.

You should setup an A record that points to your public IP (i.e. mail.company.com) and then set the MX record to ponit to mail.company.com

Oli
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Author Comment

by:WineGeek
ID: 17989374
what about a reverse DNS record for mail?
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Author Comment

by:WineGeek
ID: 17989388
If you're going to tell me I should or should not do something, please provide the why behind it. So, why should you never pint an MX record directly to an IP address and why would some mail servers fail to deliver mail in such a case? Thanks.
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Expert Comment

by:olifarago
ID: 17989390
If you want to setup a RDns record then ask your ISP that provides you with your static IP address to setup the RDns record on your IP to point to whatever A record you setup for your mail (i.e. mail.company.com).

Oli
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Expert Comment

by:olifarago
ID: 17989404
I am afriad I cannot give you any mroe information than that, it is simply invalid use of DNS, MX records should point to a FQDM as the other expert mentions above.

Perhaps someone else can shed some light?
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LVL 9

Expert Comment

by:olifarago
ID: 17989479
Hi,

I found an MS article stating that sometimes exchange 2000 will not send to hosts with MX records pointing to CNAMES or IP address.  Hope this helps a little: http://support.microsoft.com/kb/280794

Oli
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Expert Comment

by:mikeleebrla
ID: 17989814
>>So, why should you never pint an MX record directly to an IP address  and why would some mail servers fail to deliver mail in such a case?
b/c that is the say DNS was designed. you simply cannot point an MX record to an IP.  I'm sure there is an RFC or IEEE standard for this.

try to point the MX record to an IP yourself, you will notice that you can't
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Author Comment

by:WineGeek
ID: 17990033
I did point my MX record to my IP address and it let me do it. :)

But now I created another A record and pointed the MX record to that so we'll see. Thanks.
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Expert Comment

by:mikeleebrla
ID: 17990491
>>I did point my MX record to my IP address and it let me do it. :)

if you are talking about on godaddy's web management tool,,, then they don't error trap like they should.  There is no OS that will let you do this directly.  It simply isn't part of the DNS standards as indicated in the link i posted.

run "nslookup -querytype=mx microsoft.com" from command line or any other domain and you will notice MX records point to FQDNs.

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Expert Comment

by:susanzeigler
ID: 17990943
Just wanted to add a comment--please do not consider this as any type of point-related answer though.

In some systems you can point an MX to an IP but it will cause DNS errors when the zone is loaded/queried and result in lost mail. There are some systems that will even ignore the errors and attempt delivery to the IP anyway. However, it is very bad practice to do anything non-RFC-compliant even if the software lets you do it. And yes, this is all is defined in RFC 1035.
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