address_metrics_lifetime — the TTL of address metrics
address_metrics_lifetime = 1800
Address metrics store data on the quality of service to a particular target host from a particular binding; data such as the time since the last failure, and how long it takes to connect and to deliver a message. Address metrics are used to determine which of a domain's MXs to open more connections to.
address_metrics_lifetime controls how long a set of address metrics will live after last being updated. Normally this option does not need to be changed.
The default value is 1800 seconds.
address_metrics_lifetime is valid in the global scope.