Please read below & Suggest me Good Solution, I searched many tutorials but didn't get clear help so try not to provide links.

We have Exchange Server 07 Name" ac-ex" with Public & Local IP Address on Same NIC with Domain name ach.com (Exchange Server is Also a Domain Controller) and this Domain and Email accessed from Internet There is no CAS Array and Most of Users access email through MS Outlook, with URL https://ac-ex.ach.com

We Built new Data Center and other City and Prepared one Server with Installation of Exchange 2013 and Domain and in LAN this is Working fine, We have Configured another Public IP Address in this Server. 

Issue is: When we Access OWA from internet it going to Old exch Server 07 i tried to delete the record of old server from DNS but still its Going towards old Server. How to solve this issue?

I need also help regarding Creating MX records.

Are these servers in the same Active Directory Domain/FOrest or different?  That will change the below answers quite a bit.

MX Record - You will need to login to your Public DNS provider and look for your current MX record. Once you find it, you can put in the new public IP address.

For the DNS names, I would suggest using one name such as mail.company.com and point that to the new server.  also change autodiscover and other records to that name.  You will have to migrate user mailboxes and have them use this new address for the webmail and activesync setup.  Outlook will find the mailbox moves with minimal configuration.

Thanks,

Jason

Hi,

Great advice from JasonApt. However, installing Exchange on a domain controller is not recommended:
https://technet.microsoft.com/en-us/library/ms.exch.setupreadiness.warninginstallexchangerolesondomaincontroller(v=exchg.160).aspx

For your question, I want to ensure below questions, please help collect answers for further troubleshooting:
1. Do you have move all mailbox from old Exchange 2007 to Exchange 2013? If not, it will connect to old server to connect to mailbox.
2. Do you configure external owa url for new server? If not and only Exchange 2007 facing internet, OWA will connect to old server first, then proxy to 2013 whose mailbox hosted.

Here's an article about Proxying and Redirection, for your reference: https://technet.microsoft.com/en-us/library/Bb310763(v=EXCHG.141).aspx

Thanks

Thanks Both of you.

Problem is this Company don't have any information bout their Public IPs and Public DNS Provider.

They Told me Both IP Addresses are Mapped with MX Records.

They Use the Server name in all Virtual Directories, and they Don't want to change this URL.

What if i Rename the Old Server (Exchange & DC) and Make the CAS Array with name of Old Server i.e ac-ex.ach.com? are there any complications in renaming server having both Exchange and Domain?