my mail server is in the dmz zone. he is behind firewall. he has the public static address. i plan that installing the proxmox mail gateway in the dmz zone. how i configure my proxmox? i assign the public ip address of mail server to the mail gateway or i assign new ipublic ip address to the mailgateway. i must register on dns server fqdn of my mailgateway or i use fqdn of my mail server? how the senders know where is my mail server?