how to send email using SendGrid from PHP code example

Example 1: php send email with attachment

$filename = 'myfile';
    $path = 'your path goes here';
    $file = $path . "/" . $filename;

    $mailto = '[email protected]';
    $subject = 'Subject';
    $message = 'My message';

    $content = file_get_contents($file);
    $content = chunk_split(base64_encode($content));

    // a random hash will be necessary to send mixed content
    $separator = md5(time());

    // carriage return type (RFC)
    $eol = "\r\n";

    // main header (multipart mandatory)
    $headers = "From: name <[email protected]>" . $eol;
    $headers .= "MIME-Version: 1.0" . $eol;
    $headers .= "Content-Type: multipart/mixed; boundary=\"" . $separator . "\"" . $eol;
    $headers .= "Content-Transfer-Encoding: 7bit" . $eol;
    $headers .= "This is a MIME encoded message." . $eol;

    // message
    $body = "--" . $separator . $eol;
    $body .= "Content-Type: text/plain; charset=\"iso-8859-1\"" . $eol;
    $body .= "Content-Transfer-Encoding: 8bit" . $eol;
    $body .= $message . $eol;

    // attachment
    $body .= "--" . $separator . $eol;
    $body .= "Content-Type: application/octet-stream; name=\"" . $filename . "\"" . $eol;
    $body .= "Content-Transfer-Encoding: base64" . $eol;
    $body .= "Content-Disposition: attachment" . $eol;
    $body .= $content . $eol;
    $body .= "--" . $separator . "--";

    //SEND Mail
    if (mail($mailto, $subject, $body, $headers)) {
        echo "mail send ... OK"; // or use booleans here
    } else {
        echo "mail send ... ERROR!";
        print_r( error_get_last() );
    }

Example 2: get php to send email from form

<?php 
if(isset($_POST['submit'])){
    $to = "[email protected]"; // this is your Email address
    $from = $_POST['email']; // this is the sender's Email address
    $first_name = $_POST['first_name'];
    $last_name = $_POST['last_name'];
    $subject = "Form submission";
    $subject2 = "Copy of your form submission";
    $message = $first_name . " " . $last_name . " wrote the following:" . "\n\n" . $_POST['message'];
    $message2 = "Here is a copy of your message " . $first_name . "\n\n" . $_POST['message'];

    $headers = "From:" . $from;
    $headers2 = "From:" . $to;
    mail($to,$subject,$message,$headers);
    mail($from,$subject2,$message2,$headers2); // sends a copy of the message to the sender
    echo "Mail Sent. Thank you " . $first_name . ", we will contact you shortly.";
    // You can also use header('Location: thank_you.php'); to redirect to another page.
    }
?>

<!DOCTYPE html>
<head>
<title>Form submission</title>
</head>
<body>

<form action="" method="post">
First Name: <input type="text" name="first_name"><br>
Last Name: <input type="text" name="last_name"><br>
Email: <input type="text" name="email"><br>
Message:<br><textarea rows="5" name="message" cols="30"></textarea><br>
<input type="submit" name="submit" value="Submit">
</form>

</body>
</html>