Subject header is duplicated #22
Description
Summary
On Windows with PHP 7, when sending an mail message with the Sendmail transport, the subject header is duplicated.
Steps to reproduce
To reproduce the bug the sample from here can be used:
http://framework.zend.com/manual/current/en/modules/zend.mail.introduction.html
The resulting mail headers look something like this:
Subject: Test Subject
Date: Wed, 29 Jul 2015 17:33:17 +0000
From: =?UTF-8?Q?test?= test@test.com
To: test@test.com
Subject: Test Subject
Cause
In the Sendmail transport all headers (including the Subject) and the subject itself are passed to the php mail function:
$result = mail($to, $subject, $message, $headers);
The mail function then appends to the $subject to the $headers. I do not think the php mail function should handle this case because it doesn't know what subject the caller intended to use. However I believe php mail should at least issue a warning (TBD: file enhancement at https://bugs.php.net/).
Solution
Pass the headers without the Subject header to the php mail function. This is already done if the os is not Windows in the prepareHeaders. I think it should be done for Windows as well.