Send email using Sendgrid (no lib or curl needed)

sendgrid.php

<?php

define('SENDGRID_KEY', 'SG.your api key here');

function sendgrid($from, $to, $subject, $message) {
	$postdata = json_encode(
	    array(
	        'personalizations' => [
	        	[
	        		'to' => [
	        			['email' => $to]
	        		]
	        	]
	        ],
	        'from' => [
	        	'email' => $from,
	        ],
	        'subject' => $subject,
	        'content' => [ [
	        	'type' => 'text/html',
	        	'value' => $message
	        ] ]
	    )
	);

	$opts = array('http' =>
	    array(
	        'method'  => 'POST',
	        'header'  => 'Content-type: application/json'."\r\n"
	        			.'Authorization: Bearer '.SENDGRID_KEY."\r\n",
	        'content' => $postdata
	    )
	);

	$context  = stream_context_create($opts);

	return file_get_contents('https://api.sendgrid.com/v3/mail/send', false, $context);
}

sendgrid('noreply@yoursite.com', 'yourclient@email.com', 'Hello', 'Hello from us!');