What sets this remittance envelope apart from a standard 6 ¾ envelope is the extra-large flap imprint area. This is a very popular envelope for donations. The extra imprint area can be used to explain different donation levels, or simply serve as a “Thank You for Your Donation”. The 6 ¾ envelope is commonly used as an insert into booklets or newsletters when an organization is looking for a donation. They are usually self-addressed; the end user would write out their check and mail it back to the organization.