Send mail with Mailgun API version 2 and PHP. Should also work with version 3 of the Mailgun API

Mailgun PHP API with curl

define("DOMAIN", "test.se");
define("MAILGUN_API", "XXX123"); // Mailgun Private API Key

function br2nl($string) {
    return preg_replace('/\<br(\s*)?\/?\>/i', "\n", $string);
}
function mg_send($to, $subject, $message) {

  $ch = curl_init();

  curl_setopt($ch, CURLOPT_HTTPAUTH, CURLAUTH_BASIC);
  curl_setopt($ch, CURLOPT_USERPWD, 'api:'.MAILGUN_API);
  curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);

  $plain = strip_tags(br2nl($message));

  curl_setopt($ch, CURLOPT_CUSTOMREQUEST, 'POST');
  curl_setopt($ch, CURLOPT_URL, 'https://api.mailgun.net/v2/'.DOMAIN.'/messages');
  curl_setopt($ch, CURLOPT_POSTFIELDS, array('from' => 'support@'.DOMAIN,
        'to' => $to,
        'subject' => $subject,
        'html' => $message,
        'text' => $plain));

  $j = json_decode(curl_exec($ch));

  $info = curl_getinfo($ch);

  if($info['http_code'] != 200)
        return false;

  curl_close($ch);

  return $j;
}

@jonaslejon any specific reason you chose to work with Mailgun API v2?

Very useful. Works with Mailgun API v3.

Thanks for all the comments! The code has been updated to work better