From a friend who recruits at FedEx, checking these boxes will help you the most to get the call:
1. Military
2. Line Check Airman, Instructor, or other type of Evaluator Position (PCA, APD, whatever) at an airline. (ignore if you're military)
3. 2500-3500hrs PIC JET TIME (again, ignore if you're military)
The hiring game at FedEx and many/most of the Legacy Airlines is very favorable towards military pilots (good ole boys club), but you can still get in as a civilian if military service is not your thing, just takes a lot more work.