Well, first of all, I would never use "work" that way. Work is a more general term often used as a non-count noun. I would say "It is my job" however. As in, "it is my job to take care of all correspondence here". We go to work, we all have to work, work could be tiring or fun, but when I speak specifically about what I do, I talk about my job. "He works at the office. He has a lot of work to do, sometimes too much work. His job is to manage all of the employees."
I hope this helps.