Mail server concept

When your mail server is connected directly to the Internet

In cases where no NAT (Network Address Translation) is being used and where your mail server is directly connected to the Internet, you will need to provide them with the FQDN and IP address of your mail server.

Note: This is, by far, the least secure method for connecting a mail server to the Internet.

Let's say you have the following LAN configuration:

In the above example you need to give the mail server's IP address as your MX Record.

Domain name: dpetri.net

Record FQDN	Record Type	Record Value	MX Pref
mail.example.com	A	212.143.143.130
example.com	MX	mail.example.com	10

You should make sure the ISP has had all the necessary routing tables updated in order to provide Internet availability to your internal IP network range.

Note: It doesn't matter if the real host name of the mail server is NOT "mail". Internet hosts don't mind that, they just need to know what's the name of the mail server, and what's the IP address for that name.