Why? It's obvious that you want to send the right thing to the right people. They'll think that you are communicating with them, not someone else. When they think like that, it's more likely that they will open your emails.
When? It's also a tricky question though. I think that when you have enough resource to mange your email marketing campaign, and your list is big enough to do this (>1,000 in my opinion).
What? You may want to segment your customer list based on few conditions that you want for example:
- Gender
- Age
- Location
- Purchase habit
- Interest
- Birthday
- ...
How? There are many methods to do this; however, it's better if you know what information you need to collect your email marketing list at the beginning. If you don't, there are many ways that help to collect more information of your current email marketing list:
- Send an email and ask them directly
- Conduct a survey or contest
- Integrate with another platform such as, Google Analytic, social media or eCommerce sites
- ...
Have a nice day :)