Question : DNS + MX record

I have configured my MX record as following . I have 2 SMTP servers

SMTP Server 1 ==> NAT IP 1 ==> MX record value = 10
SMTP Server 2 ==> NAT IP 2 ==> MX record value = 10

So both the servers are loadbalanced using the MX record of equal priority for incoming traffic.

In case if 1 of my server fails how the DNS will update the MX record stating that server 1 fails & how it will recogonise not to send the traffic to server 1

Answer : DNS + MX record

I admit I'm slightly confused about why you would NAT one public IP behind another, but it's not really relevant as long as the TCP packets make it to the mail server and back.

Chris