1: YOUR E-MAIL ADVERTISING SOFTWARE MUST BE FEATURE RICH, BUT EASY TO USE
In case your e-mail marketing applications overcomplicate things or do not provide a user experience, you will burn an unlimited amount of time tinkering and problem-solving. You want an extended feature set and increased flexibility, for sure, but that should not come at the expense of ease-of-use.

The e-mail marketing software I like, Onlinemailcampaign, proves that you could Package functions and flexibility in a system while maintaining simplicity.