exim and MX records

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exim and MX records

Postby Thasaidon » Mon Aug 15, 2011 2:41 am

Hi,

recently I've registered some new domains, because a lot of ISP's were refusing mail from my free domains (no-ip and dyndns).
However, by registering these new domains, I now also have MX records (mail.mydomain.net)

Is it nececary to configure this in Exim somewhere? Maybe as primary mail domain? Or is it sufficient to just have an MX record referring to my A record in DNS?

Thanx in advance
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Re: exim and MX records

Postby Island » Mon Aug 29, 2011 12:54 pm

Thasaidon, I cannot answer your question absolutely, but I can say that I configured my Exim to have island.dyndns.org as the domain name for which it had to relay/acceot mail, so I would guess that you still have to do that with your new name.

But I am thinking about the same problem, myself. I notice you had been using dyndns etc; Could I ask you if you are using a dynamic IP for your new registration? I am assuming you are not but, if you are, how do you arrange the DNS record updating etc?. (I am still learning about this.)

regards, Island
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Re: exim and MX records

Postby Thasaidon » Mon Aug 29, 2011 1:16 pm

Hi Island.

I use different domains for my webserver and mailserver.
The webserver used to be a dyndns.org domain and the mailserver used a no-ip.org domain.
In my mailserver I used the mydomain.no-ip.org domain, and I now use my new mydomain.com
I was just wondering if I should use mail.mydomain.com too.

If you have a dynamic IP, you can use Freesco to update the dyndns or no-ip domains automatically when your IP changes
You can do this via the setup menu and is fairly easy to setup.
However, I don't use this option because I have a fixed ip, so I manually "activate" my domains each month.
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Re: exim and MX records

Postby Island » Mon Aug 29, 2011 4:57 pm

Thasaidon wrote:In my mailserver I used the mydomain.no-ip.org domain, and I now use my new mydomain.com
I was just wondering if I should use mail.mydomain.com too.


Thasaidon, I hesitate to comment because I think you are 'ahead' of me but, I notice that various ISPs use quite different (DNS-resolvable) names for their mailservers, and these names must be in their MX records. Let me give some examples:

send.vodafone.net
mail.vodafone.net
pop.gmx.net
relay.clara.net
smtp.tesco.net
etc .. ..

So, I conclude from this that what is important is:
(i) that the mail server is routable-to, and
(ii) the actual name of the entry in the MX record does not matter - provided that the name resolves to a routable address

For example, if you have a (routable) separate IP address for your mail server, you can give it any name you wish, and set the MX record appropriately.

Alternatively, if the mail server is on a non-routable address, you can set the MX record to the whichever router is directly reachable (routable to), and then use 'port forwards' to reach your mail server (this is what I have to do on one of our gateways, and using a dynamically-assigned IP in the manner you describe).
Now, what this means (to me, in particular) is that all I have to do is make sure that even if our mail server is using a non-routable address, I have the necessary 'port forward' implemented so that the server is reached from the resolved domain name.

Now, because you can always 'port forward' when you wish, you have the choice whether to have a second DNS-entry for the mail server, particularly. It is not necessary, I understand (though the RFCs should be closely checked). I receive mail perfectly well using Exim, on FREESCO, with simply using names such as nemo@island.dyndns.org

In your case - running Exim on FREESCO, then even if you had a 'separate' name for your mail server, it would resolve to the same address.

My guess is that you already knew this - all this - so the only thing I would say is that as I understand it (from the dyndns help files) the RFCs do NOT require that the MX record is a separate name or a separate address. Indeed, they seem to suggest the MX record can be blank (though I have also seen comment that many organisations will - wrongly - reject mail from such domains).

Thasaidon wrote:However, I have a fixed ip, so I manually "activate" my domains each month.


Indeed, I've looked at the dyndns site about this, because we have been offered a service with a static address. Dyndns will disable static accounts UNLESS they are updated within:
not less than 26 days, and
not more than 30 days.
And they mean it; on their forum are several comments from customers who have been 'caught out' by this. To be fair, they also give examples of dyn DNS clients which can be set for 'periodic' updates; I have not (yet) checked whether the FREESCO client can do this. (It may not matter, anyway; we could run the client they recommend on one of our Linux machines behind FREESCO, and thus keep dyndns happy.)

regards, Island
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Re: exim and MX records

Postby Lightning » Tue Aug 30, 2011 6:15 am

Dyndns will disable static accounts UNLESS they are updated within:
not less than 26 days, and
not more than 30 days.
And they mean it; on their forum are several comments from customers who have been 'caught out' by this. To be fair, they also give examples of dyn DNS clients which can be set for 'periodic' updates; I have not (yet) checked whether the FREESCO client can do this. (It may not matter, anyway; we could run the client they recommend on one of our Linux machines behind FREESCO, and thus keep dyndns happy.)
The dyndns client in the 04x series is compliant with the dyndns requirements and will not let a domain expire due to lack of an update or get you marked for abuse due to to many updates. You do however have to enable a cron job for dyndns to accomplish this with a semi-static or static IP. Then it is completely automatic with no manual updates needed.
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Re: exim and MX records

Postby Thasaidon » Tue Aug 30, 2011 9:22 am

Island wrote:My guess is that you already knew this - all this - so the only thing I would say is that as I understand it (from the dyndns help files) the RFCs do NOT require that the MX record is a separate name or a separate address. Indeed, they seem to suggest the MX record can be blank (though I have also seen comment that many organisations will - wrongly - reject mail from such domains).

Well my knowledge here isn't that far ahead of you :D
All my domains and MX record point to the same public IP, which is on eth0 on my Freesco.
So like you, my conclusion was that it wouldn't matter if I used mydomain.com as primairy e-mail domain or mail.mydomain.com
but I just wanted to check here ;)

As for the DynDNS client in Freesco I knew it was there, but I didn't know it could also update on regular intervals...
I just clicked in the "still active" link in the e-mails I got when they were about to expire.
But now my no-ip and dyndns will expire, because I registered some "real" domains.

but thanks for all the input :)
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Re: exim and MX records

Postby Island » Tue Aug 30, 2011 4:55 pm

I hope the conclusion is correct! May I take the opportunity to ask you one more - somewhat related - question?

Thasaidon wrote:All my domains and MX record point to the same public IP


Are you running your own nameserver? Or did you obtain a nameserver-service via the provider of your new domain name?

I have been looking at a free domain name system, here:

http://www.eu.org/

but I think, when using this, I would nevertheless need to provide TWO nameservers, each of which have to be on different IP addresses. I think (I might be wrong) that means, in practice, that you would have to run BIND on port 53 on your LAN, and also run BIND somewhere else (or borrow an entry in someone else's BIND). Did you ever look at this? (There are also some remarks, in passing, about MX records, by the way.)

regards, Island
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Re: exim and MX records

Postby Thasaidon » Wed Aug 31, 2011 8:09 am

I'm not running any DNS servers myself.
I registered my domains at a hosting provider.
When I change my ip or my redirects, they make sure it's updated in DNS, which is almost instantly.

As for eu.org,
I looked into that once, but I too was under the impression I needed to run my own DNS servers, which I don't want.
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