This is a quick hack which allows sending files from a mautic form as mail attachment.

mautic_files_via_sendgrid.php

<?php

// This is a quick hack which allows sending files from a mautic form as
// mail attachment.
// We use sendgrid for sending the mail.

// Please note: Since this was a one-off workaround, some customizations are needed:
// Line 27: check for the correct form id
// Line 33-36: Replace 12…15 with your form field id
// Line 50: Enter your sendgrid api key
// Everywhere: Replace „attachment_X“ with your form field name

class webhook {
	public function getRequest()
	{
		$rawData = file_get_contents("php://input");
		return json_decode($rawData);
	}

	public function sendMail($requestData) {
		$submissionData = $requestData->{'mautic.form_on_submit'}[0]->{"submission"};

		$id = $submissionData->id;
		$formid = $submissionData->{"form"}->{"id"};

		// Only trigger for form id 2
		if($formid != 2) {
			die();
		}

		$results = $submissionData->results;

		$a1 = dirname(__FILE__) . "/media/files/form/" . $formid . "/12/" . $results->{'attachment_1'};
		$a2 = dirname(__FILE__) . "/media/files/form/" . $formid . "/13/" . $results->{'attachment_2'};
		$a3 = dirname(__FILE__) . "/media/files/form/" . $formid . "/14/" . $results->{'attachment_3'};
		$a4 = dirname(__FILE__) . "/media/files/form/" . $formid . "/15/" . $results->{'attachment_4'};

		$html = "
			<p>You've got some files:</p>

			Attachment 1: ".$results->{'attachment_1'}."<br>
			Attachment 2: ".$results->{'attachment_2'}."<br>
			Attachment 3: ".$results->{'attachment_3'}."<br>
			Attachment 4: ".$results->{'attachment_4'}."	
		";


		$url = 'https://api.sendgrid.com/';
		$user = 'api_key';
		$pass = 'SENDGRID_APIKEY';

		$params = array(
			'to'        => 'to@example.com',
			'subject'   => 'You’ve got files',
			'html'      => $html,
			'from'      => 'from@example.com',
		);

		if(is_file($a1)) {
			$params['files[a1_'.$results->{'attachment_1'}.']'] = new CURLFile($a1);
		}
		if(is_file($a2)) {
			$params['files[a2_'.$results->{'attachment_2'}.']'] = new CURLFile($a2);
		}
		
		if(is_file($a3)) {
			$params['files[a3_'.$results->{'attachment_3'}.']'] = new CURLFile($a3);
		}
	
		if(is_file($a4)) {
			$params['files[a4_'.$results->{'attachment_4'}.']'] = new CURLFile($a4);
		}
		


		$request =  $url.'api/mail.send.json';
		$header[] = 'Authorization: Bearer '.$pass;
			
		$session = curl_init($request);
		curl_setopt ($session, CURLOPT_POST, true);
		curl_setopt ($session, CURLOPT_POSTFIELDS, $params);
		curl_setopt($session, CURLOPT_HEADER, false);
		curl_setopt($session, CURLOPT_SSLVERSION, CURL_SSLVERSION_TLSv1_2);
		curl_setopt($session, CURLOPT_RETURNTRANSFER, true);
		curl_setopt($session, CURLOPT_HTTPHEADER,$header);
		$response = curl_exec($session);
		curl_close($session);
	}
}

$webhook = new webhook;
$requestData = $webhook->getRequest();
$webhook->sendMail($requestData);