Email goes to spam using by PHP Mailer and wp_mail

Question

Duplicate question. I found some answers but no one works.

I want to send email using Php Mailer or wp_mail with attachment PDF file in WordPress. In both techniques PHP Mailer or wp_mail, Email goes with attachment but every time in spam.

Code using PHP Mailer 1

$mail->From = "from email";
$mail->FromName = "name";
$mail->AddAddress("to email");
//$mail->AddReplyTo( 'from email', 'name' ); //Line add or not doesn't effect.
$mail->AddAttachment("filename.pdf");    
$mail->Subject = "Email Subject";                  
$mail->Body = "Email Body";
if(!$mail->Send())
{
   echo "Message could not be sent. <p>";
   echo "Mailer Error: " . $mail->ErrorInfo;
}
else
{
   echo "Message sent";
}

Code using PHP Mailer2

$mail->isSMTP();                                      
$mail->Host = 'smtp.gmail.com';  
$mail->SMTPAuth = true;                             
$mail->Username = 'email user name';                 
$mail->Password = 'password';                                          
$mail->Port = 587; //587 or 25


$mail->From = "from email";
$mail->FromName = "name";
$mail->AddAddress("to email");
//$mail->AddReplyTo( 'from email', 'name' ); //Line add or not doesn't effect.
$mail->AddAttachment("filename.pdf");    
$mail->Subject = "Email Subject";                  
$mail->Body = "Email Body";
if(!$mail->Send())
{
   echo "Message could not be sent. <p>";
   echo "Mailer Error: " . $mail->ErrorInfo;
}
else
{
   echo "Message sent";
}

Code using wp_mail

global $wpdb;
$to = 'to email';

$from = 'from email'; 
$name = 'name';
$headers = 'From: name <from email>' . "\r\n";

$subject = 'SUBJECT';

$msg = 'CONTENT';

$mail_attachment = array('filename.pdf');   
wp_mail($to, $subject, $msg, $headers, $mail_attachment);