diff --git a/system/libraries/Email.php b/system/libraries/Email.php
index ebff756..034586a 100644
--- a/system/libraries/Email.php
+++ b/system/libraries/Email.php
@@ -1469,6 +1469,20 @@
 	 */
 	protected function _prep_quoted_printable($str)
 	{
+		// ASCII code numbers for "safe" characters that can always be
+		// used literally, without encoding, as described in RFC 2049.
+		// http://www.ietf.org/rfc/rfc2049.txt
+		static $ascii_safe_chars = array(
+			// ' (  )   +   ,   -   .   /   :   =   ?
+			39, 40, 41, 43, 44, 45, 46, 47, 58, 61, 63,
+			// numbers
+			48, 49, 50, 51, 52, 53, 54, 55, 56, 57,
+			// upper-case letters
+			65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90,
+			// lower-case letters
+			97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122
+		);
+
 		// We are intentionally wrapping so mail servers will encode characters
 		// properly and MUAs will behave, so {unwrap} must go!
 		$str = str_replace(array('{unwrap}', '{/unwrap}'), '', $str);
@@ -1516,14 +1530,25 @@
 				$ascii = ord($char);
 
 				// Convert spaces and tabs but only if it's the end of the line
-				if ($i === ($length - 1) && ($ascii === 32 OR $ascii === 9))
+				if ($ascii === 32 OR $ascii === 9)
 				{
-					$char = $escape.sprintf('%02s', dechex($ascii));
+					if ($i === ($length - 1))
+					{
+						$char = $escape.sprintf('%02s', dechex($ascii));
+					}
 				}
-				elseif ($ascii === 61) // encode = signs
+				// DO NOT move this below the $ascii_safe_chars line!
+				//
+				// = (equals) signs are allowed by RFC2049, but must be encoded
+				// as they are the encoding delimiter!
+				elseif ($ascii === 61)
 				{
 					$char = $escape.strtoupper(sprintf('%02s', dechex($ascii)));  // =3D
 				}
+				elseif ( ! in_array($ascii, $ascii_safe_chars, TRUE))
+				{
+					$char = $escape.strtoupper(sprintf('%02s', dechex($ascii)));
+				}
 
 				// If we're at the character limit, add the line to the output,
 				// reset our temp variable, and keep on chuggin'