How to configure smtp_fallback_delay in postfix 2.6
 

Hi Admins,

How to configure smtp_fallback_delay in the same server. I have two instances in which I would like to fall back the deferred mails to the other instance/backup and the other is used exclusively for sending.
Please help me out to configure

All Postfix parameters are documented at http://www.postfix.org/postconf.5.html. The description of smtp_fallback_relay says the following about configuring a fallback relay on the same computer:

With bulk email deliveries, it can be beneficial to run the fallback relay MTA on the same host, so that it can reuse the sender IP address. This speeds up deliveries that are delayed by IP-based reputation systems (greylist, etc.).

The fallback relays must be SMTP destinations. Specify a domain, host, host:port, [host]:port, [address] or [address]:port; the form [host] turns off MX lookups. If you specify multiple SMTP destinations, Postfix will try them in the specified order.

In your case, I guess the domain of your fallback instance could be the right choice.