Using post status transitions to send custom alerts (in WP Job Manager)

Something I get asked a fair bit with regards to my plugins is how to send an alert during an event, for example, “when a job expires in WP Job Manager, how can I notify the user?”

Plugins which use custom post types, like WP Job Manager, are likely to use custom/standard post statuses too – it’s pretty common. Using these statuses you can easily hook-in a custom function and trigger and email.

This is a quick tutorial for hooking into a status change and sending an email for WP Job Manager.