Letters are great in the business-to-business marketing environment as a lead generation device as they are more likely to reach the decision-maker than a postcard which may be intercepted by the gate-keeper. It also allows you to add additional inserts like forms, full color brochures or business cards.

Depending on what you are selling, in a business to consumer setting, letter mailers which are personalized and have more privacy than a postcard can also close the sale for small ticket items. This may not be easy with a postcard or brochure.

For more complex products or services both in a business or consumer setting, letter mailers should be used primarily to generate leads.