=== modified file 'modules/system/mail.sending.inc'
--- modules/system/mail.sending.inc	2009-11-02 05:00:03 +0000
+++ modules/system/mail.sending.inc	2009-11-06 14:32:32 +0000
@@ -48,7 +48,9 @@ class DefaultMailSystem implements MailS
     $line_endings = variable_get('mail_line_endings', MAIL_LINE_ENDINGS);
     return mail(
       $message['to'],
-      mime_header_encode($message['subject']),
+      // The email might not be sent properly if the subject field contains
+      // newline characters.
+      str_replace("\n", ' ', mime_header_encode($message['subject'])),
       // Note: e-mail uses CRLF for line-endings. PHP's API requires LF
       // on Unix and CRLF on Windows. Drupal automatically guesses the
       // line-ending format appropriate for your system. If you need to