If you're worried that an email blast to your list on behalf of a third party will increase unsubscribes, then here's an original solution. Business 2 Community newsletter allowed Constant Contact to include a tweetable "Tip of the Week" in its newsletter. All other content was editorial and helpful. This is a much softer sell, and possibly a lower price point for advertisers. It's a great way to test how your readers will respond to third party messages....