Internet-connected Exchange Servers
When connecting your Exchange Server to the Internet it is important to make sure that your domain's MX Record is resolvable. You should contact your ISP for this. Give your FQDN and IP address of your mail server.
Mail server is directly connected to the Internet
Here no NAT is being used and mail server is directly connected to the Internet, you will need to provide them with the FQDN and IP address of your mail server.
Let's say you have the following LAN configuration:
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Here the mail server's IP address as your MX Record for domain name:- windowsadmin.info as given
FQDN Record Type Record Value MX Pref
mail.windowsadmin.info A 212.143.143.130
windowsadmin.info MX mail.windowsadmin.info 10
Let NAT is being used
Here you will need to provide the IP address of your external NAT interface, and configure your NAT device with Static Mapping for TCP Port 25, and have all TCP Port 25 traffic forwarded to the internal IP address of your mail server.
Let a Mail Relay is being used
Here you will need to provide the FQDN and IP address of your Mail Relay machine, and configure the Firewall to only allow TCP Port 25 traffic to be sent to the Mail Relay's IP address, not to your real mail server.
You should then configure the Mail Relay to forward the incoming e-mail traffic to the real mail server (after scanning it for spam, viruses and so on).
