I am using contact form 7 in my site, but it alway return "Failed to send your message. Please try later or contact the administrator by another method." error message when i submit form. When i remove your $headers in includes/classes.php line 550 it's ok. Why?
Also when i set true in debug option of wordpress is return notice about UPLOADS constant when active. Can you fix it?
<b>Notice</b>: Use of undefined constant UPLOADS - assumed 'UPLOADS' in <b>...wp-content/plugins/contact-form-7/includes/functions.php</b> on line <b>179</b>