Thomas Waymouth invented a machine to manufacture self-gummed envelopes in the late 1860s, according to the National Postal Museum. A pair of brothers, Daniel and Henry Swift, later invented a machine to automate the manufacture of self-gummed envelopes, allowing for faster production.
Envelopes were not frequently used in the early days of American mail because senders paid for each piece of paper they sent. Most individuals sealed letters by folding and adding a wax seal. In the 1840s, postal reform standardized the cost of postage, applying a flat rate based on distance and weight. This change inspired senders to use envelopes because they were included in the postage price, and several companies began manufacturing envelopes to meet demand.