Direct mail letters are great for lead generation, producing impressive response rates of up to 15.1%. If you’re looking to boost your sales, letters can also function as your top salesperson to generate results around the clock.. Your Personalize mail letters get the word out about your business, advertise products and services, and more with 8-1/2” x 11” full-color, uncoated paper and a #10 Standard-face envelope. Plus, letter personalization and envelope addressing comes part and of the package with complete mailing services.