Some advice about using emaillists

Hi there,
i have a small problem.
i recently got a list with about 15k local email adresses and i would love to use them for marketing
but here emails must be with opt-in and i dunno if they are.
last week i tried a mailing with roundabout 1,5k emails and just got 2 letters from lawers trying to make me pay a fine... sorry, don't know how to explain it right in english, but i think u know the message.

is there a way to use those 15k emails without getting slammed by lawers?

Your new album has just been released, or maybe you've just booked a huge show. Time to email everybody you know! Before you add your entire address book to the "To:" field of a new email, consider a few points of email list etiquette. By respecting the recipients of your mass emails, you'll have far better results from your efforts, build stronger relationships with your fans,

i did respect the etiquette in my mailings.
it's just a normal newsletter