Quick note: two bugfixes

[micschk]

MailgunMailer.php around line 220; fix check for valid email adresses
(may be multiple and/or formatted as "Sender Name" <sender@company.tld>)

        // We need _at least_ one valid $to addresses
        $to_email_arr = explode(',', $to);
        $to_email_formatted = array_shift($to_email_arr);
        $to_email_parts = explode('<', $to_email_formatted);
        $to_email_address = trim(str_replace('>', '', array_pop($to_email_parts)));
        if ( ! filter_var($to_email_address, FILTER_VALIDATE_EMAIL)) {
            user_error('MailgunMailer::sendMailgunEmail invalid $to [' . $to . ']', $err_type);
            return false;
//            $from = Email::config()->get('admin_email');
        }
        // We need a valid $from address
        $from_email_parts = explode('<', $from);
        $from_email_address = trim(str_replace('>', '', array_pop($from_email_parts)));
        if ( ! filter_var($from_email_address, FILTER_VALIDATE_EMAIL)) {
            // ... and throw error if still invalid
            user_error('MailgunMailer::sendMailgunEmail invalid $from [' . $from . ']. Maybe set a default Email.admin_email in yaml config?', $err_type);
            return false;
        }

MailgunMailer.php around line 250; leave Reply-To headers in peace

//            if (array_key_exists('Reply-To', $customHeaders)) {
//                $replyTo = $customHeaders['Reply-To'];
//                unset($customHeaders['Reply-To']);
//            }