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I have a web server needs connection from external/internal location, but just opening a port, by NAT Port Forwarding, may not good enough as far as I experienced in MikroTik router - you cannot connect to your server by domain name. Following configuration enables you to connect to your local server by domain name like you do on external network.
Note that you should check 
like above
To enable above on your MikroTik router, you should drag and drop as #1 item on your NAT list like below:
Other references helpful
Policy Based Routing - https://wiki.mikrotik.com/wiki/Policy_Base_Routing