What are the country laws regarding getting started with email marketing if I am scared?

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What are the laws and regulations regarding email marketing in the countries I reside in? Are the guidelines mostly standard or do they vary from country to country? How do private data protection acts affect email marketing? Is email marketing illegal in certain countries? Do I need to consult a lawyer for advice on email marketing laws, and if so, is there a way to do so without incurring a large expense? Do I need to register as a marketing firm instead of an individual to comply with the laws?