DNS and Web Hosting

Hello Experts,
I need to host a web site for one of the companies we own, so I setup their external DNS server to use my Public IP, then I setup IIS and my firewall. the web site works remotlly only.
But I also need to manage the site, so I added theirDomain.com as a zone to my DNS server and setup a A record with the site internal IP. After doing that, the site is working fromt he outside and the inside network which is a good thing.
However, I cannot get to any of the sites they hosting on their own, I cannot email them.
What I am doing wrong?
Who is Participating?
b_levittConnect With a Mentor Commented:
At the point you made a copy of theirDomain.com on your internal DNS server, that DNS server became "authorative" for that domain.  So when you request mail.theirDomain.com, your server says "unknown host" and looks no further since it beleives it's the single point of truth.

This is often referred to as "split dns".  The easy way to fix this is to duplicate the records they have to your internal dns server.

If you don't want to maintain two copies of the domain, another option is to create a special internal domain.  For example you could use hosts or a subdomain of your domain, ie: theirDomain.yourDomain.com.

The disadvantage is the different urls when internal vs external, but that might beat coordinating dns changes.
Did you setup a MX record for their SMTP gateway?
rfinalyAuthor Commented:
No I did not, so I need to add an MX record for their Exchange server on the zone I created for them? also do I need to add all of the sites that they still hosting that I will be able to access them? is there any other solutions.
Thank you

If you want to access any website with name then you have to setup every website DNS zone and that website nameserver (You can manage nameservers from domain control panel) should point to DNS Server (Where you have DNS files).

Regarding MX you have to set it in your DNS zone. The DNS file format should be as follows (The following DNS File includes website, FTP and Mail Records)

@      86400      IN SOA      ns1.nameesrver.com. hostmaster.domain.com. (
                         2008080501    ; Serial number
                         3600          ; Refresh
                         900           ; Retry
                         604800        ; Expire
                         14400       ) ; Minimum TTL
domain.com            NS      ns1.nameserver.com.
domain.com            NS      ns2.nameserver.com.
Domain.com            A      xx.xx.xx.xx (Your website IP)
Domain.com            MX      1 mail.domain.com
*.domain.com            A      xx.xx.xx.xx (Your website IP)
ftp            A      xx.xx.xx.xx (Your FTP Server IP)
mail            A      xx.xx.xx.xx (Your mail server IP)
www            A      xx.xx.xx.xx (Your website IP)

I think I understood your question in wrong manner, Please refer my following post for the same:

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