http://www.rfc-editor.org/rfc/rfc1652.txt
RFC 1652: SMTP Service Extension for 8bit-MIMEtransport, J. Klensin, N. Freed, M. Rose, E. Stefferud, D. Crocker1994-07-01T23:00:00-00:00This memo defines an extension to the SMTP service whereby an SMTP content body consisting of text containing octets outside of the US- ASCII octet range (hex 00-7F) may be relayed using SMTP. [STANDARDS-TRACK]