Quoted-printable, or QP encoding, is an encoding using printable characters (i.e. alphanumeric and the equals sign "=") to transmit 8-bit data over a 7-bit data path. It is defined as a MIME content transfer encoding for use in Internet e-mail.
http://en.wikipedia.org/wiki/Quoted-printable

quoted-printable: caracterele ASCII imprimabile pot fi transmise direct, iar celelalte se codeaza sub forma =XX, unde XX reprezinta valoarea caracterului, scrisa in baza 16. Se foloseste pentru texte ce cuprind cateva caractere speciale (indeosebi texte folosind caractere cu diacritice, de exemplu in ISO-8859-1)
http://www.cs.ubbcluj.ro/~rlupsa/edu/retele-2003/c3.html