Use the Mail Options Web page to specify how to manage e-mails and to define configuration information used in processing incoming and outgoing e-mails.
If you specify a mailbox gateway, all outbound e-mails are sent to the gateway for delivery to the destination.
If you do not specify a mailbox gateway, the configured Domain Name server is used to look up the host.domain portion of the outgoing user@host.domain e-mail address.
If the DNS lookup fails, the administered host file entries are checked for this host.domain.
If these methods fail, the message is marked as undeliverable and returned to the sender.