Index: library/Zend/Mime.php
===================================================================
--- library/Zend/Mime.php	(revision 23462)
+++ library/Zend/Mime.php	(working copy)
@@ -127,33 +127,43 @@
         $lineEnd = self::LINEEND)
     {
         $out = '';
-        $str = self::_encodeQuotedPrintable($str);
-
-        // Split encoded text into separate lines
-        while ($str) {
-            $ptr = strlen($str);
-            if ($ptr > $lineLength) {
-                $ptr = $lineLength;
-            }
-
-            // Ensure we are not splitting across an encoded character
-            $pos = strrpos(substr($str, 0, $ptr), '=');
-            if ($pos !== false && $pos >= $ptr - 2) {
-                $ptr = $pos;
-            }
-
-            // Check if there is a space at the end of the line and rewind
-            if ($ptr > 0 && $str[$ptr - 1] == ' ') {
-                --$ptr;
+        
+        if (function_exists('quoted_printable_encode')) {
+            // Only available in PHP 5.3 or greater
+            $out = quoted_printable_encode($str);
+        } elseif (function_exists('imap_8bit')) {
+            // Requires IMAP Module
+            $out = imap_8bit($str);
+        } else {
+            $str = self::_encodeQuotedPrintable($str);
+    
+            // Split encoded text into separate lines
+            while ($str) {
+                $ptr = strlen($str);
+                if ($ptr > $lineLength) {
+                    $ptr = $lineLength;
+                }
+    
+                // Ensure we are not splitting across an encoded character
+                $pos = strrpos(substr($str, 0, $ptr), '=');
+                if ($pos !== false && $pos >= $ptr - 2) {
+                    $ptr = $pos;
+                }
+    
+                // Check if there is a space at the end of the line and rewind
+                if ($ptr > 0 && $str[$ptr - 1] == ' ') {
+                    --$ptr;
+                }
+    
+                // Add string and continue
+                $out .= substr($str, 0, $ptr) . '=' . $lineEnd;
+                $str = substr($str, $ptr);
             }
-
-            // Add string and continue
-            $out .= substr($str, 0, $ptr) . '=' . $lineEnd;
-            $str = substr($str, $ptr);
+    
+            $out = rtrim($out, $lineEnd);
+            $out = rtrim($out, '=');
         }
-
-        $out = rtrim($out, $lineEnd);
-        $out = rtrim($out, '=');
+        
         return $out;
     }