I’ve recently created USPS tracking module for Drupal, so Qwintry.com users could get notifications when their international packages change state. I’ve used queue operations to build requests to USPS API by cron, and it seems to work great for our customers, but this story is not about the module.

My plan was to provide rules event “The package [tracking number] changed active state from [old state] to [new state]”. (words in square brackets are Rules arguments).

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