Unfortunately, organizations often lack a large enough list size of former donors to perform statistically - significant tests to see what will make your former donors give more or less. (epolitics.com)
Plans are often free to start but can grow to hundreds of dollars a month, depending on email list size and volume. (entrepreneur.com)
Authors can use it to search for prospective book promotion services, sorting by genre, advertising costs, and mailing list size. (bookworks.com)