Well we would like to setup our own exchange server at work,so I was going to finish the exchange setup onto our main server at work here . However before I do this, I need to figure out how to configure the DNS, A record, and MX records on ctsindia.com under our domain name srikarn.org.
Now I do not know what to change on ctsindia.com so that it points to our external IP (example 123.45.67.142) so that it can get access to our exchange server? I also need to keep it that when people type www.srikarn.org it goes to that ip address 59.90.242.189 to access to the company hosting our website.
Now our ISP is from bsnl (dataone). We currently have a static ip with them of 59.90.242.189 . Is there anything else I need to do with them for me to get this exchange server live onto the internet?
I really hope someone can clear up what I am supposed to put onto ctsindia.com..
I feel like you're over-thinking this and confusing some details. Instead of trying to directly answer your questions as asked, let's focus instead on what is necessary to receive Email from the Internet. This may be more detail than you need, or over-simplified for your current understanding.
First you need a registered domain name. For Email, that will be represented by the @company.org in the address. When outside mail systems want to send a message to @company.org, it queries the public DNS for the public IP address to which to send.
The public IP address is returned by the use of two DNS record types. The first is the MX record. This links a fully qualified domain name (FQDN) and a priority value in the range of 0-255. The lowest valued MX record is returned. The second DNS record type is the A record. This links a FQDN to an IP address. At a minimum, you can have a single A record and a single MX record to establish an Email presence.
With these two DNS entries, and with your mail server accessible via the 123.123.123.123 address, outside systems will be able to send mail to you. This is the simplest configuration, and there are nuances with DNS that can be utilized for advanced functionality, but this is the basic information you need.