试试这段代码吧，解码mime 的

 function decode_mime_string ($string) {
   $pos = strpos($string, @#=?@#);
   if (!is_int($pos)) {
     return $string;
   }
   
   $preceding = substr($string, 0, $pos); // save any preceding text
   
   $search = substr($string, $pos+2, 75); /* the mime header spec says this is the longest a single encoded word can be */
   $d1 = strpos($search, @#?@#);
   if (!is_int($d1)) {
     return $string;
   }
   
   $charset = substr($string, $pos+2, $d1);
   $search = substr($search, $d1+1);
   
   $d2 = strpos($search, @#?@#);
   if (!is_int($d2)) {
     return $string;
   }
   
   $encoding = substr($search, 0, $d2);
   $search = substr($search, $d2+1);
   
   $end = strpos($search, @#?=@#);
   if (!is_int($end)) {
     return $string;
   }
   
   $encoded_text = substr($search, 0, $end);
   $rest = substr($string, (strlen($preceding . $charset . $encoding . $encoded_text)+6));
   
   switch ($encoding) {
   case @#Q@#:
   case @#q@#:
     $encoded_text = str_replace(@#_@#, @#%20@#, $encoded_text);
     $encoded_text = str_replace(@#=@#, @#%@#, $encoded_text);
     $decoded = urldecode($encoded_text);
     
     if (strtolower($charset) == @#windows-1251@#) {
       $decoded = convert_cyr_string($decoded, @#w@#, @#k@#);
     }
     break;
     
   case @#B@#:
   case @#b@#:
     $decoded = urldecode(base64_decode($encoded_text));
     
     if (strtolower($charset) == @#windows-1251@#) {
       $decoded = convert_cyr_string($decoded, @#w@#, @#k@#);
     }
     break;
     
   default:
     $decoded = @#=?@# . $charset . @#?@# . $encoding . @#?@# . $encoded_text . @#?=@#;
     break;
   }
   
   return $preceding . $decoded . decode_mime_string($rest);
} // decode_mime_string()

原文转自：http://www.ltesting.net