In-flight magazines, sponsored by airlines, were one of the first custom media and remain typical of the genre.
Such out-sourced services can be limited to design and editorial responsibilities or include the complete production and distribution process.
In addition, many of the companies sell advertising space within custom publications to third parties; this subsidizes the cost of publication; creates a more authentic editorial environment; and allows third parties to purchase and publicizes an association with the media's sponsor, while reaching that sponsor's customers (e.g. food suppliers may purchase advertising space within a supermarket's custom media).
This is accomplished by providing information and, often, advice, that meets the needs and suits the preferences of the sponsor's target market.
It serves the interests of the audience, rather than overtly plugging products and services the way ads do.