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Thread: DNS help - where to create "A" and "MX" records

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    Default DNS help - where to create "A" and "MX" records

    I am having a lot of success installing my first Zimbra system, but I realise that I am lacking in my knowledge of DNS. I have been using another mail server (Mailtraq) for many years and for various reasons I have not needed to understand very much about DNS, beyond simple nslookup queries etc.

    The reason is effectively because I have always used ISPs, from whom our incoming e-mail has been collected via POP from a global email address for our domain, but in the ISP's server. Also, I have always used a 'smarthost' for outbound mail.

    Rightly or wrongly, these are the methods I have used before and they have worked very well for me.

    Having said this, I know in a larger commercial installation that incoming mail should be routed via an MX record on the domain, and that sending mail from the mail server is usually performed by look-ups on recipients' MX records. However the latter in particular has always been nothing but trouble for me, so I have avoided it and used a 'smarthost'.

    But I now find myself getting to know Zimbra and clearly needing to understand the DNS requirements more so than before.

    At this moment I am setting up a trial system for myself to use and for testing purposes. I need it for training and testing only. Therefore I do not want mail delivered to this Zimbra test machine using an MX record on my domain. This is because I do not want to affect my mail already being handled on another system. Also I do not want to register a new domain solely for trying Zimbra - it seems unnecessary. Therefore I just want to pick up 'test' mail from a POP mailbox out on the Internet.

    The guide for Zimbra clearly indicates that Zimbra requires an "A" record and an "MX" record: "Configure DNS. In order to send and receive email, the Zimbra MTA must be configured in DNS with both A and MX records..."

    (1) Where is this referring to? Is it referring to one's domain zone records, or to the hosts file in Linux? My /etc/hosts file is as follows:

    127.0.0.1 localhost.localdomain localhost
    192.168.0.131 dell-desktop.samidomain.com dell-desktop

    I have also seen elsewhere the following example. Again, where would this be set up? (2) On the Linux box, or in the domain zone records?

    [...]
    mail.example.com. A 1.2.3.4
    mail.example.com. MX 0 mail.example.com.
    example.com. MX 0 mail.example.com.
    [...]


    Notwithstanding my wish to set up a test system, I still need to fully understand these DNS settings for when the production server is put into place! Therefore I cannot rest on my laurels once I have got my test machine working! Thanks for any help in advance. I have tried to research DNS as far as possible but most of what I've read is theory only - not enough hard detail.

  2. #2
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    Both types of records, A and MX, are going to be on your DNS servers (in your zone records) for your domain name. It is also advisable to put the local server's information in the /etc/hosts - some things also look here.

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    Thanks for the quick reply p24t. Ok, I understand that in production we will need our A and MX records pointing correctly, but where does the following get applied? I have found this in a how-to, but not showing where it should be applied.

    [...]
    mail.example.com. A 1.2.3.4
    mail.example.com. MX 0 mail.example.com.
    example.com. MX 0 mail.example.com.
    [...]

    Also, in my initial test system I want to collect mail from a POP mail account rather than have it directed at my machine. Is there any information that can help with that, and in particular help me with any DNS settings locally on my machine, that might need to be done?

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    Right, those A and MX records need to go on the DNS server, in the zone records for the domain.

    Not sure about the POP. If you create an account, you can attach an external POP account to it, and retrieve the mail that way. I don't know if there's a way to use fetchmail or anything of the sort.

  5. #5
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    Quote Originally Posted by p24t View Post
    Right, those A and MX records need to go on the DNS server, in the zone records for the domain.

    Not sure about the POP. If you create an account, you can attach an external POP account to it, and retrieve the mail that way. I don't know if there's a way to use fetchmail or anything of the sort.
    There is, I use it all the time. Once you have installed fetchmail (obviously), far and away the easiest way to get it to check your external account is to install Webmin and then use Webmin's fetchmail administration applet to set up a fetch for your pop account. Then Webmin also lets you schedule automatic checking, and puts in a cron job for you, all from the GUI. WAY easier than any other method I've seen.
    Cheers,

    Dan

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