It is impossible to answer that question without knowing what you are trying to do.

• Why do you have two appliances?
• How are they being used?
• Why do you need to make SMG know each other?

As Kevin already replied. Usually you will create a SMG network. So all appliances work together and store configuration, data and values in common databases. 

If you have started to install two separate appliances they will use two separate databases which do not communicate ...

I am new to SMG and GW.

We are planning to use two SMG for load-balancing ie. We are having LB in front of  SMG so with LB will manage traffic to both node.

Why do you need to make SMG know each other?

any cluster type (heartbeat)

I under stood

in this i have added the details of 2nd SMG also.

They have to know each other to use the same database in the background. Otherwise you have to check each server's quarantine, tracker information and so on.

If you more than one appliance (cluster, load balancing, ...) than add a SMTP Interface to each server, but only one holds the quarantine.

Some examples (in use at customers).

Customer A: 5 appliances. Main server holds quarantine, tracker and statistics. 2 appliances for inbound, 2 appliances for outbound traffic. IMAP scanning is distributed among the last for servers.

Customer B: 8 appliances. Main server holds quarantine, tracker and statistics. 2 appliances for inbound, 4 appliances for outbound traffic (there is a special request to distinguish GroupWise mails (GWIA hop) and "SMTP" mails (i.e Thunderbird hop)). And there is a separate server just for IMAP scanning.

I understood so no need to configure the details on other server since both are standalone SMG. That is why the second node showing down