BUG #14994: Email alert

On Sat, Dec 30, 2017 at 07:14:02AM +0000, PG Bug reporting form wrote:

How to set auto Email alert after failure slave node in Streaming
Replication please suggest me.

This is usually the kind of job where a monitoring process running
checks periodically is fit for. You should do things on both the
primary, by for example looking at pg_stat_replication, and the standby
by looking at its status and how its WAL receiver goes, which is where
the new system view pg_stat_wal_receiver becomes handy.
--
Michael