822date - print the date in a mail message
822date reads an 822-format mail message from its standard input, and
prints the 822-format date shown in the last header field named name,
or Date if name is not supplied.
822date prints the date in three forms: first, ISO format,
using the time zone shown in the field; second, ISO format, using UTC;
third, ctime format, using the local time zone. Beware that most
ctime libraries do not correctly handle leap seconds or years past
2037.
822field(1), 822received(1), ctime(3)