Havent tried this to our t-shirt company Yourcupoftee but we also run a print office and we bought not the list itself but the service of a mass email when we released a new website, it was said to reach about 200 000 emails. It didnt bring a single order and altho it might build some recognition for the future I would avoid it unless you can get a really good deal on the list and know its focused on emails in your clientele.
My tip would be to build a email list of people who sign up just like people above suggested, then you know these people will have an interest in your product and you dont have to spend/waste money on lists that not necessary will give you anything.