How long is breast milk good for?

How long does breast milk last in the freezer?
I plan to EXCLUSIVELY breast feed for at LEAST the first month.
I will be pumping once I'm confident my sons latch is good and nipple confusion is out of the question.
I am 39+1 weeks and want to start pumping and building up a supply within a week AFTER he's born.
How long is breast milk still good after freezing?