Once you have a database of customers you can segment and group them. This enables you to track which people are most responsive to certain offers and therefore target the right people in the future. Some segmentation occurs automatically according to customer behaviour, top 20 customers for example, but you can also create and control grouping.
You may want to consider what segmentation is helpful for your organisation, for example you notice that students tend to come into your bar on week nights and professionals come in at weekends. You could target students by segmenting your database according to “Date of birth” or “Company”.
You can tag customers into as many groups as you like. Don’t worry about people being sent duplicate emails if they are in more than one group they will only receive one email.