Try changing your headers to this:
$headers = "MIME-Version: 1.0" . "\r\n";
$headers .= "Content-type: text/html; charset=iso-8859-1" . "\r\n";
$headers .= "From: successive.testing@gmail.com" . "\r\n" .
"Reply-To: successive.testing@gmail.com" . "\r\n" .
"X-Mailer: PHP/" . phpversion();
For a few reasons.
One of which is the need of a Reply-To
and,
The use of apostrophes instead of double-quotes. Those two things in my experience with forms, is usually what triggers a message ending up in the Spam box.
You could also try changing the $from
to:
$from = "successive.testing@gmail.com";
EDIT:
See these links I found on the subject https://stackoverflow.com/a/9988544/1415724 and https://stackoverflow.com/a/16717647/1415724 and https://stackoverflow.com/a/9899837/1415724
https://stackoverflow.com/a/5944155/1415724 and https://stackoverflow.com/a/6532320/1415724
http://www.webhostingtalk.com/showthread.php?t=931932
"My host helped me to enable DomainKeys and SPF Records on my domain and now when I send a test message to my Hotmail address it doesn't end up in Junk.
It was actually really easy to enable these settings in cPanel under Email Authentication. I can't believe I never saw that before.
It only works with sending through SMTP using phpmailer by the way. Any other way it still is marked as spam."
PHPmailer sending mail to spam in hotmail. how to fix
http://pastebin.com/QdQUrfax