Tracking # is not populating (86909)

I've configured inbound email services for Stat to pickup and create CSR. The created CSR is not populating the Tracking # from the inbound email. What is the logic to configure the Tracking # Identification from Electronic Mail Interface Setup for label:value like XYZZ:C123456?

1. From Electronic Mail Interface Setup window, click on Tracking # Identification tab.

2. In the Match Regular Expression field: (XYZZ:\s*\w*) then click Add button. This will be added to the Match String. Be sure that the added string is Move UP to the top of the list.

3. In the Test Sting field, enter XYZZ:C123456 then click Test button. It should returns Found Match - XYZZ:C123456