8BITMIME
The 8BITMIME extension was standardized in 1994. It facilitates the transparent exchange of e-mail messages containing octets outside the seven-bit ASCII character set. Prior to the availability of 8BITMIME implementations, mail user agents employed several techniques to cope with the seven-bit limitation, such as binary-to-text encodings (including ones provided by MIME) and UTF-7. However, each of these workarounds inflates the required amount of data for transmission of non-ASCII text. Some non-ESMTP servers allowed the sending of 8-bit characters, but it is risky to send such data to a server whose 8-bit capabilities are unknown.
In March 2011, 8BITMIME was published as RFC 6152 corresponding to the then new STD 71.
Read more about this topic: Extended SMTP