UTF-7
From Just Solve the File Format Problem
UTF-7 is a 7-bit encoding of Unicode which is intended for use in transports (e.g., some email gateways) that cannot safely transfer character codes with the high bit set (0X80 through 0XFF). It is compatible with ASCII except that the character "+" is used as a shift code.
In addition to the IANA charset code UTF-7 (MIBenum 1012), there is an earlier version designated as charset UNICODE-1-1-UTF-7, alt csUnicode11UTF7, MIBenum 103.
