Revisiting MX and A records

> As my saga to setup OWA continues, I have been asked by the ISP:
>
> what is the mailserver hostname to use for the MX record and what
> would you like us to set the preference to?

Well – that really has nothing to do with OWA specifically. Your domain’s MX
record is how the rest of the world finds the server which hosts mail for
your Internet domain name.

Whomever hosts the domain’s public DNS (which may not be the same as the
ISP; that term generally mean “the company I pay for my Internet
connectivity) will needs to set up:

1. An A (address) record, such as mail.mydomain.com – which specifies
your/the correct public IP
2. Your domain’s MX record then specifies that A record, at the lowest
cost/highest priority

Once this is done, and you’ve got inbound traffic on TCP port 25 forwarded
to your Exchange server’s LAN IP, *and* you’ve got @mydomain.com in your
recipient policy via the CEICW you ran, you will be hosting your own mail.
http://www.msexchange.org/tutorials/MF002.html explains how this works.

Then – since you’ve only got one Exchange server, and you’ve already got a
nice easy-to-remember A record for it, you can forward TCP port 443 to your
internal IP – and your users can use https://mail.mydomain.com/exchange (or
/remote…) if you’ve enabled this in the CEICW.
>
>
> Do we just ask them to setup a fictitious name like
> “johnzwebmail.john.com,

No.

> or do we need to use an actual registered web
> name?

Domain name, yes. You don’t have to, but you won’t be able to do much in OWA
without that….you’ll just have internal / intra-office mail.

> if our domain is www.ourdomain.com

Well, the above isn’t a domain – the domain there is ourdomain.com. www is a
host on that domain (it’s an A record).

> , do we need to register the
> domain name mail.ourdomain.com and then point the MX record at that?
>

You’d register a domain name, then have its DNS configured as per the above.

> or is this question asking what the machine name (or IP address) of
> the mailserver is?

Not sure I understand….but I think, no.

>
> Thanks for any and all help.

> One thing I am still unsure about from #1 below: do I need to
> register the domain name “mail.mydomain.com”

No. As said before, mail.mydomain.com is not a domain name – mydomain.com is
a domain name. “mail” is a host on that doman.

mail.mydomain.com needs to be created as an A record (not a CNAME/alias) in
mydomain.com’s  public DNS.

> or since I already have
> a domain name can I just add the word “mail” to it?

Whomever hosts your public DNS will do this. Unless you have access to a
control panel of sorts, that is. Given that you seem not to have much
experience with DNS, it would probably be safer to work with the company who
hosts the domain’s DNS to have them do it.
>
> So if the domain name I ahve is johnzdomain.com, do I also need to
> register mail.johnzdomain.com?

No.


***


correct, forget about the function of the machines (www, mail, FTP,
whatever). DNS is just a way of allowing names to access IP’s.

You own a domain, domain.com.
Host or “A” records in the domain point to IP addresses. The A record for
the SBS public IP can be any word, ‘mail’ makes sense only because you will
be using it for such, it could be ‘office’ (office.domain.com) or ‘location’
(location.domain.com) or ‘ahugestringofgobbledegook’
(ahugestringofgobbledegook.domain.com).

AN MX record points to a name, normally a host or ‘A’ record but this is
also not the only choice. The name simply needs to resolve to an IP address.
Of course, if you use the name for the MX record it’s necessary to have a
mail server working on whatever IP that name addresses.


***


….actually, an MX record *must* specify an A record – not an IP address,
and not a CNAME …. as per the RFCs…


***


If your hosting your own SMTP mail server then you need a mx record that
points to your mail server within your organization. A machine name is not
required for an mx record. Most companies will use something like

mail.comapnyname.com

You will usually use the same name as your company. The IP address they are
requesting is the external IP of your network. So when some sends an email
to joeblow@yourcomapnyname.com it will be sent directly to your Exchange
server.

The preference thay are referring to I beleive a better term is the
“priority”. Some companies have more than one mx record so setting the
priority is essential as to which mail server it goes to first. Myself we
use our mail hosting providor as a backup. So my mx record has a lower
priority than their mail servers. What this means is that if my mail server
goes down then it will route it to the next priority which is their backup
mail server and will stay there until my mail server comes back online.


***


In addition to A and MX records, you should/must have a “PTR” record, aka
“reverse dns”.  Many ISPs, and the list is growing, will not allow mail to
enter their system unless they can trace it back to its point of origin.
There is also a SPF record, but their use is not universal as of yet.

Have a look at www.dnsstuff.com.  Put in some real names, and some phony
names and you will get the idea.  Although the big button in the middle ask
you to pay, there is a free registation below and to the right.

Larry Struckmeyer


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