What do your subscribers want from you? Usually, when they signed up with you they had some expectations: you promised something.
You need subscribers who can expect high end material from you. That’s what you want, but many companies choose to ignore expectations.
You either mail too frequently and annoy subscribers or you mail too little and don’t capitalize on your chance to interact with them.
Not all email programs fall into these categories, but many do.
The problem is email marketing is still a bit a separate discipline, where “more” is annoying and a “little” is forgettable.