[Sami]

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.