Outlook Mailer: header name ‘Precedence’ should start with ‘x-‘ or ‘X-‘.

Replies: 0

Using Outlook Mailer:
InvalidInternetMessageHeader: The internet message header name ‘Precedence’ should start with ‘x-‘ or ‘X-‘

Full error log:
From: Name<myemail@hotmail.com>
Reply-To: myemail@hotmail.com
Message-ID: <gUsFMWztr23cFBs7aPT5zA78BP6ljTUQArKeXJB38k@myhostingaccount.com>
X-Mailer: WPMailSMTP/Mailer/outlook 2.5.3
Precedence: bulk
X-Newsletter-Email-Id: 12
X-Auto-Response-Suppress: OOF, AutoReply
MIME-Version: 1.0
Content-Type: multipart/alternative;
boundary=”b1_gUsFMWztr23cFBs7aPT5zA78BP6ljTUQArKeXJB38k”

any thoughts?
On test email works very well. When sending to multiple subscribers (as test) i have the error above.

Thank you!