As per all marketing, it is about empathy. Every recipient has a different perception of your brand due to the rapport you have with them and their experience of your brand.
Obviously you can’t write one email per person so you ‘normalise’ it. Each person gets categorised depending on what we think their perception is based on experience, path of entry, interaction etc. Some categories might be different but might have a a very similar perception and can be merged.
At the end of it all you will have a group of categories with different groups of perceptions. At the very least you are likely to have Customers and Prospects. You might be able to break prospects down depending on how much interaction they have with you. The same might be said of customers, although if they are a frequent buyer, blog commenter, etc. etc. you might be able to less formal than you are with someone who buys once or twice a year.
You then decide how you want to communicate with these groups of people and write different messages or content blocks.
Does this seem familiar? It sounds like profiling again only with copy and not content!
This is something that is often missed. We decide how are brand says and phrases things and we do it consistently, we then change the content to make sure each person gets the email that they are most likely to respond positively to but we never consider changing the felling of our words!
Worth a thought, I do write differently to friends than I do strangers and it is the same with customers and prospects depending on how they are. A customer that I hardly ever hear from will be written to formerly while a prospect that I have a laugh with but just can’t close the deal will get swear words!