How fine should the grind of espresso be?

I have my own espresso machine and I get my espresso beans from Starbucks. I also have them grind it for me. I bought a pound yesterday and they ground it, but it looks finer than usual, almost looks like powder. I paid no mind to it cause I know espresso grind should be very fine, but I used it in my espresso machine, and what do you know it, it drips out very slowly as if the water can't even seep through. What am I doing wrong? or is my espresso grind wrong?