If you are considering an e-mail blast, newsletter campaign, or other written communications with potential customers, it is very important what you DON'T write.
Obviously, you should know (and if you don't, here's a tip) that using unsolicited lists is wrong. I won't belabor the many reasons why, but they range from breaking the law to breaking down a good relationship. Your lists should be clean, and going to those who have at least given tacit approval they want some form of marketing communications.
So – you have a good, clean list. And you really, really want to sell something. Now obviously, you can't write each piece to each individual customer. So you are going to need to use some genetic copy, along with some assumptions when you write.