early 15c., in ceramics, "a vitrified substance, either transparent or opaque, applied as a coating to pottery and porcelain," from enamel (v.). As "hardest part of a tooth," 1718, from a use in French émail.
Even aerial navigation in 1999 was found too slow to convey and deliver the mails. The pneumatic tube system was even swifter, and with such facilities at hand it is not surprising that people in San Francisco received four daily editions of the Manhattan journals, although the distance between Sandy Hook and the Golden Gate is a matter of 3,600 miles. ["Looking Forward," Arthur Bird, 1899]
Associated Press style guide collapsed it to email 2011.