mail(): SMTP server response: 550-"JunkMail rejected - email

Question

I Would like to send email using contact form in my company website,
I was set the email configuration in php, here is my form :
<form action="sendmail.php" method="post" class="form form--contacts">
<input type="text" name="name" class="form__input" placeholder="Name" required>
<input type="email" name="email" class="form__input" placeholder="Email" required>
<input type="text" name="subject" class="form__input" placeholder="Subject" required>
<textarea class="form__textarea" name="text" placeholder="Text"></textarea>
<input class="form__btn" name="send" type="submit" value="Send">
</form>
and here is sendmail.php :
<?php
if($_POST['send']){
$admin = 'myname#mydomain.co.id';
$name = htmlentities($_POST['name']);
$email = htmlentities($_POST['email']);
$subject = htmlentities($_POST['subject']);
$text = htmlentities($_POST['text']);
$headers = 'MIME-Version: 1.0' . "\r\n";
$headers .= 'From:'.$name.' <'.$email.'>' . "\r\n";
$headers .= 'Content-type: text/html; charset=iso-8859-1' . "\r\n";
$pengirim = 'From: '.$name.' <'.$email.'>';
if(mail($admin, $subject, $text, $headers)){
echo 'SUCCESS: Mail Successfully sending';
}else{
echo 'ERROR: Error Sending Email';
}
}else{
header("Location: index.php");
}
?>

Answer 1

There might be few reasons for junk mail detection.
First, you don't have "To: " in your headers.
Second, you rely on your system mail and you have no control over from which account you are sending mail from. If your "From:" header is different than your actual "mail from:" in your SMTP connection it's a red flag for spam filter.
You should try using PHPMailer instead of built in function. ( https://github.com/PHPMailer/PHPMailer ) or other alternative.
Some info may be found in this post: Sending email with PHP from an SMTP server