This page describes how Projectrak subscriptions work. Since Projectrak 6.6.0, you'll be able to see an "envelope" icon, that upon selection will allow you to subscribe to a PQL query that you have used to filter through your Jira projects.
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How to schedule a new subscription
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When there's a change in one of the Projects that you have subscribed to in the PQL, the next subscription notification will show the changes that have been made in the project fields, only if you have chosen the "Highlight updated values since the last email notification" option in the configuration screen. 