The first postal-sanctioned airmail flights were made in 1911. On May 15, 1918, the Post Office Department instituted the world's first regularly scheduled airmail flights. The National Postal Museum has a number of envelopes carried on some of the most historic and fascinating flights of the early years of airmail service.
1918 - Woodhouse cover
1911 Earle Ovington cover
1918 First Flight - Taussig Cover (May 15, 1918)