phpmailer go directly to Gmail's trash basket - phpmailer

Question

Hi there this Friday afternoon!
I work with an email script using phpmailer.
But when will show the email in gmail, it to Trash instead. But while in hotmail will email instead of the inbox. I have Googled it but can not find anything.
My code:
$mail = new PHPMailer;
//$mail->SMTPDebug = 3; // Enable verbose debug output
$mail -> isSMTP();
// Set mailer to use SMTP
$mail -> Host = 'mailcluster.loopia.se';
// Specify main and backup SMTP servers
$mail -> SMTPAuth = true;
// Enable SMTP authentication
$mail -> Username = 'my username';
// SMTP username
$mail -> Password = 'my password';
// SMTP password
$mail -> SMTPSecure = 'tls';
// Enable TLS encryption, `ssl` also accepted
$mail -> Port = 587;
// TCP port to connect to
$mail -> CharSet = "UTF-8";
$mail -> From = 'my from mail';
$mail -> FromName = 'Axelan';
$mail -> addAddress($email, $gamename);
// Add a recipient
$mail -> addReplyTo('my add to mail', 'Axelan replay');
$mail -> WordWrap = 50;
// Set word wrap to 50 characters
$mail -> isHTML(true);
// Set email format to HTML
$mail -> Subject = 'Tack för din registering!';
$mail -> Body = 'Hej ' . $gamename .'!
<p>Aktivera ditt konto genom att följa denna länk</p>
<p>Inloggnings uppgifter:<br>
<b>Användarnamn/email:</b> ' . $email . '<br>
<b>Lösenord:</b> ' . $p['string'] . '</p>';
$mail -> AltBody = 'This is the body in plain text for non-HTML mail clients';
if (!$mail -> send()) {
echo $mail->ErrorInfo;
} else {
$book = array('reg' => 'ok', 'message' => '');
echo json_encode($book);
}

Answer 1

It is up to each email service provider to implement spam filtering how they wish. It is not a black and white, correct or incorrect way of doing things. There are always spammers trying to circumvent spam filtering to get their messages in front of human eyes. As such, spam filtering is always changing and updating. It's a moving target.
It may even be based on your IP address. If your email server is hooked up to an IP that has been used by spammers in the past, the IP may be blacklisted as an IP that spam originates from. The spammers have now moved on, and left you with a dirty IP.
Two good things to do to minimize the "spamminess" of your messages is to implement SPF records in your DNS entries, as well as set up DKIM