Part of the problem is that people are confused about the difference between ‘strategy' and ‘tactics'. It's essential not to get these two confused. They are related – tactics are a vital part of what makes a strategy work – but they’re not the "be all and end all." Too many people neglect a full and comprehensive strategy in favour of a bunch of loosely-connected tactics. So, to recap:

Demographics: Certain demographics like age, gender, job title, and other information that informs your buyer personas can be a good way to segment customers and customize messages. For example, a financial company may want to send retirement-themed emails to customers seeking information on offering their employees benefits and emails about college loans to university-based customers.
My next answer:                                                                                                                    - You see, - I could easily charge $100 or even $200 for a copy of this unique Self-Send-Solo System, - but why shoul I? My main income are made from other websites I own, not from this one here - this one here is more for fun and of course I make money from sales, (after all I am a business man)
Technology has a significant impact on consumers’ expectations, and those expectations impact how subscribers engage with your email marketing. Brands need to continually demonstrate that they know their customer, which can make it a challenge to stay on top of the evolving context of marketing. An email strategy can make all the difference between building a relationship with your customers and sinking without trace.