Answer:
Sends paper without using the post office.
A man goes out in heavy rain with nothing to protect him from it. His hair doesn't get wet. How does he do that?
I go around in circles, But always straight ahead Never complain, No matter where I am led.
They come in many varieties: Red, Black, Dead, and Caspian to name a few.
It carries paper of the most important sort but also plastic, I'm glad to report. What is it?
I am the fountain from which no one can drink. For many I am considered a necessary link. Like gold to all I am sought for, but my continued death brings wealth for all to want more.