Analyze your data sources with a 4-step plan Door EmailGarage op 7 augustus 2014 in Email Marketing, Opt-in, Tips One of the key drivers to successful email marketing is a lively and ever-expanding database. And to make their database grow, most brands use multiple ways to harvest new data. This is of course a good way to do it. But in the rush of setting up new data flows, we sometimes forget to add the data source. But why is it so important to add a data source?