We have been shifted to a new office environment, where everything is setup properly. We are using Windows Server 2012 R2, and I am facing one issue with it.
My domain control for the internal name is example.com, and my email and website use the same domain name, example.com. For the website, this works when using www, but for the email in Outlook, when connecting to the domain, the mail is getting stopped. When I turned off the DNS, email worked fine. Please help me with this problem.
Actually, everything is not setup properly. Your problem is that your Active Directory domain is setup incorrectly. It should be setup as a subdomain of your externally facing domain, not with the same name. Because your Active Directory domain has the same name as your publicly facing domain, internal clients connect to your Active Directory domain and use its DNS entries, rather than the DNS entries contained on your publicly facing nameservers.
Based on what you've described, your domain controllers do not have the correct DNS entries for your email service, which is why internal clients can't get email unless you shut down your internal DNS.
The proper way to fix this is to fix Active Directory - migrate your Active Directory domain to a subdomain of your externally facing domain - but you can also workaround the problem to some degree by copying the DNS entries from your external domain into your Active Directory-hosted DNS.
You need to configure your server in a split DNS's way.
From Wikipedia;
In computer networking, split-horizon DNS, split-view DNS, split-brain DNS, or split DNS is the facility of a Domain Name System (DNS) implementation to provide different sets of DNS information, selected by, usually, the source address of the DNS request.
This facility can provide a mechanism for security and privacy management by logical or physical separation of DNS information for network-internal access (within an administrative domain, e.g., company) and access from an unsecure, public network (e.g. the Internet).
That force you to keep both zone updated correctly.
Like if www.example.com if hosted externally, then internally you must create the record to point to the correct IP, and if from example you got a exchange server on an internal IP, then internally it will be ok, but in the outside DNS you must set the same record to your public IP where OWA is accessible.
