Content-Transfer-Encoding: base64

Base64 encoding is the scheme used to transmit binary data. Base64 processes data as 24-bit groups, mapping this data to four encoded characters. It is sometimes referred to as 3-to-4 encoding. Each 6 bits of the 24-bit group is used as an index into a mapping table (the base64 alphabet) to obtain a character for the encoded data. The encoded data has line lengths limited to 76 characters. The characters used in base64 encoding, the base64 alphabet, include none of the special characters of importance to SMTP or the hyphen used with MIME boundary strings.