What laws affect email marketing?

I'm about to set up a new email marketing system for my business, and want to be sure I don't fall foul of the law. What laws do I need to know about?

Alasdair Taylor's answer to What laws affect email marketing? (562791349)

Answer to the question: 

At present the most important pieces of UK legislation for email marketers are the The Privacy and Electronic Communications (EC Directive) Regulations 2003 and the Data Protection Act 1998. The Regulations do not affect the requirements of the Act, and accordingly you need to ensure your email marketing campaigns are compliant with both sets of rules.