We also could file 'thank you / attaboy' paperwork for our colleagues, both in our own department or ones we interacted with. Those were just as valuable (if not more) than ones from the customers.
Over the years (11) during my employment there I received a couple of good letters, and they were recognized by the management in a very sincere way.
To this day of & when I have an extraordinary collaboration with someone in the corporation I'll take the time to write a thank you letter to their manager.
It's just a great practice that harkens back to the old adage, "there's nothing better than a nice handwritten thank you card." Since I'm in management, it serves as a nice means to to move the needle for a colleague in the eyes of the company.