I've used tripwire for years, but since I rarely configure it I always have to read back up on some of the tutorials I have on how to properly set it up.

One thing that almost every tutorial misses is how to actually make Tripwire email reports when run. They all cover where to put the email addresses and settings, but most skip how to actually trigger that to happen. You must use a specific command line argument to cause Tripwire to send the actual report.

So, here it is for future reference:

tripwire --check --email-report