https://github.com/zendframework/zend-mail/issues/64

diff --git a/src/Header/HeaderWrap.php b/src/Header/HeaderWrap.php
index df532ed..e0be2f5 100644
--- a/src/Header/HeaderWrap.php
+++ b/src/Header/HeaderWrap.php
@@ -116,7 +116,21 @@ abstract class HeaderWrap
      */
     public static function canBeEncoded($value)
     {
-        $encoded = iconv_mime_encode('x-test', $value, array('scheme' => 'Q'));
+        // avoid any wrapping by specifying line length long enough
+        // "test" -> 4
+        // "x-test: =?ISO-8859-1?B?dGVzdA==?=" -> 33
+        //  8       +2          +3         +3  -> 16
+        $charset = 'UTF-8';
+        $line_length = strlen($value) * 4 + strlen($charset) + 16;
+
+        $preferences = array(
+            'scheme' => 'Q',
+            'input-charset' => $charset,
+            'output-charset' => $charset,
+            'line-length' => $line_length,
+        );
+
+        $encoded = iconv_mime_encode('x-test', $value, $preferences);
 
         return (false !== $encoded);
     }