What is that job called when you deliver mail with a cart within an office? (10pts!)?

you are not a post person (I think), you see it in movies all the time you use these kind of carts.

http://cache3.asset-cache.net/xc/2000667



Also if you can please tell me the qualifications for becoming one, Thanks in advance!
The title varies a bit by company, but Mail Room Clerk is the basic title.
post boy