DNS Help
TERM | DEFINITION |
DNS | A distributed Internet directory service. DNS (Domain Name Server or System) is used primary to translate between domain names and IP addresses, and to control Internet email delivery. |
Start of Authority (SOA) | Contains information about the domain that was given to Internic when the domain was registered. It contains several record types, in particular 'NS', 'MX', and possibly an 'A' record. |
Name Server (NS) | NS records are part of the SOA and contain names of your domains name servers. |
Mail Exchanger (MX) | "MX" records are found in the SOA record and there they provide the names of the mail servers in your domain. MX records will also be found outside of the SOA. |
Address (A) | Establish the name of the host and its IP address. Provides the IP address when the hostname is requested. |
Reverse (PTR) | PTR records provide a backwards IP address to name conversion. The PTR provides the hostname when the IP address is requested. |
DNS and IMail.
1) Register your domain name with
Internic or your ISP provider.
2) Secure a static IP address for you server.
3) Configure your Network Server
4) Setting Up IMail
5) DNS
6) Troubleshooting
1) Decide upon a domain name. If you are not sure whether the domain name you have chosen is taken or not, then you can verify it at this website: http://www.domainsforbeginners.com/ . Once you have secured your DNS name then you must register it with either Internic or any Domain Name Registration provider. Here is a list of DNS Registration providers from Internic: http://www.internic.net/alpha.html
2) You must have at least 1 static IP address for your IMail server. The IP address you use is very important to how the DNS records will be implemented. The IP address will come from your ISP or backbone to the internet.
3) This IP address must be the primary IP address bound to your NIC card. Your Primary domain will use this IP address.
4) Setting Up IMail
There are several fields in IMail that will reflect your network settings.
For Instance, NT is configured with a machine name and IP address that
is used when setting up a domain in IMail. I will use Ipswitch.com as my domain
name and the machine name is IMAIL. The IP address will be 121.1.0.1
Using IMail virtual host Admin there are three fields that need to be filled
that will be used when setting up your DNS records.
a) Official Host Name:
The "Official
Host Name" is usually a combination of your MACHINE NAME
and DOMAIN NAME. So in this case our official host name
will be: IMAIL.IPSWITCH.COM.
NOTE: The Official Host Name does not have to include your machine name. If I wanted to, I could have called this starwars.ipswitch.com or used any other name in combination with my domain name. As long as you set up the DNS records in relation to the name you give, IMail will work correctly. |
Click for Screenshot |
b) Select an IP address:
IP ADDRESS | Click for Screenshot |
You will select your primary address as shown in Picture 1. |
c) Virtual Host Alias:
Host Alias | Click for Screenshot |
The Host Alias will be the domain name alone. |
Once your domain is set up in
IMail, then the DNS records must be in place in order for your domain
to function properly.
5) Setting up the DNS records
Taking the information we have already from the above screen shots:
Domain Name - Ipswitch.com
Mail server ip address - 121.1.0.1
Official Host Name - imail.ipswitch.com
You can then proceed to creating your DNS records.
a) Whenever you create a new DOMAIN, you must begin with a SOA (Start of Authority Record).
IPSWITCH.COM Explanation
- SOA
IN NS HUB.IPSWITCH.COM Explanation - The name server for IPSWITCH.COM . The
NAME SERVER will be the actual server that your records will reside on. Also
known as your DNS server or the machine you will be creating the records on.
This can be the same machine your IMail is installed on; however, many ISPs
choose to have a separate server for this service.
b) Next comes the "MX" record. The MX record is needed to display the official mail server for the domain.
IN MX 10 IMAIL.IPSWITCH.COM Explanation - The number after "MX" indicates the priority level. If you have more than one mail server, this number will increment. The lower number will take priority.
c) Next the "A" record. The "A" record is needed in order to resolve the official host name to an IP address.
IMAIL IN A 121.1.0.1
d) Some server will not accept mail from you unless your domain has a PTR record. A PTR (reverse lookup) record allows receiving domains to identify a domain name by querying the IP address.
1.0.1.121 IN-ADDR.ARPA IN PTR IMAIL.IPSWITCH.COM
In the end your DNS records would look something like this:
IPSWITCH.COM | Will contain the "MX" record | IMAIL.IPSWITCH.COM |
IMAIL.IPSWITCH.COM | Will Contain the "A" record | 121.1.0.1 |
121.1.0.1 | Will contain a PTR record | IMAIL.IPSWITCH.COM |
How it Works:
If I was to send a message to user@ipswitch.com, then this is what happens before my message is actually received by the recipient.
Mail server tries to resolve domain name. In this case, the message is going to ipswitch.com. IMail will first query the DNS server (assigned in the SMTP tab of IMail Administrator) for an "MX" record. The DNS server should then reply back with:
IN MX 10 IMAIL.IPSWITCH.COM
Once the official host name is found, IMail will then Query the "A" record for IMAIL.IPSWITCH.COM. The DNS server should then respond back with:
IMAIL.IPSWITCH.COM IN A 121.1.0.1
IMail will then know to try and contact 121.1.0.1 to deliver the message via SMTP.
Some domains at this point will perform a PTR (reverse lookup) to make sure that they are not being spammed. In this case, they would query 121.1.0.1 to make sure that IP belonged to IMAIL.IPSWITCH.COM.
As you can see by the process above, if any part of the DNS record is wrong (spelling, wrong IP), the delivery of the message will fail.
6) Troubleshooting
Some domains such as AOL require you have an additional PTR record in order
for them to accept mail from your domain. In short, before accepting mail from
your server they will query your mail servers IP address to make sure it matches
the domain name that the incoming email is claiming to come from. The PTR record
simply provides a backwards IP address to name conversion. For a more detailed
explanation of PTR records, please see this web site: http://www.intac.com/~cdp/cptd-faq/section2.html#input
Even though the DNS records for a domain may be correct, the mail server may not be able to contact the DNS server (Network trouble, service down) to resolve the domain address which would also cause the delivery to fail.
Declude, listed below, also has some good tools to run a check against your DNS to see if the records have been implemented properly. You can also utilize WS_Ping ProPack to check your DNS records. If using WS_Ping ProPack you will need to use the lookup portion of this utility to verify your DNS records.
In the picture below you will see the type of responses you should receive in this utility.
The names in the yellow square should be used in the (name or IP address box) and the Query type is highlighted in the blue box. One exception is the IP address. The address should be entered as normal in the "Name or IP address box" such as in this instance: 121.1.0.1. However, the query response will reverse the numbers such as 1.0.1.121 as shown here. This is normal.
The two most popular DNS packages are DNS BIND and Microsoft DNS. Below are helpful resource pertaining to both:
BIND - http://www.isc.org/Products/BIND/
Microsoft DNS - http://www.microsoft.com/technet/winnt/winntas/technote/implemntintegra/dns0197.asp
Links
- DNS Central
Information on registering a domain name - HowStuffWorks
A DNS tutorial - WebServer Compare
A Layman's Guide to the Domain Naming System - DNSSTUFF
Tools to check your DNS - DNSREPORT
Tools to check your DNS