The mailing universe for this retired military audience is finite and the client was experiencing "list fatigue" with their direct mail program, meaning the prospects were responding at a much lower rate than previously.
Changed the format to an engaging envelope package that contained brochure content on a colored letterhead insert. Also used personalized URL (PURLs) and increased data personalization in the letters.
The client's response rate increased by 3X with the first mailing and the same mailing program has been used in various forms for three+ years.