Access the Control Panel of your DNS host provider
After you’ve configured the external URL on the Mailbox server virtual directories, you need to configure your public DNS records for Autodiscover, Outlook Web App, and mail flow. The public DNS records should point to the external IP address or FQDN of your Internet-facing Mailbox server and use the externally accessible FQDNs that you’ve configured on your Mailbox server. The following are examples of recommended DNS records that you should create to enable mail flow and external client connectivity.
|FQDN||DNS record type||Value|
Should you have one, click here