Bu kodları dener misin.

$mail2 = new PHPMailer();
$mail2->SMTPDebug = 0;
$mail2->SMTPAuth = true;
$mail2->SMTPSecure = 'ssl'; 
$mail2->Host = $host['value'];
$mail2->Username = $user['value'];
$mail2->Password = $password['value'];
$mail2->Port = $port['value'];
$mail2->setLanguage("tr", "phpmailer/language");
$mail2->CharSet = 'UTF-8'; 
$mail2->isHTML(true);
$mail2->SetFrom($user['value'], $user['value']);
$mail2->addReplyTo($user['value'], $user['value']);
$mail2->AddAddress($adminMail['value']);
$mail2->Subject = "Yeni Navlun Talebi";
$mail2->Body = '
    <html>
        <head>
            <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        </head>
        <body>
            <h1>Yeni Navlun Talebi</h1>
            <p>Yeni bir navlun talebiniz var.</p>
            <br><br>
            <p>İsim: '.$firstname.'</p>
            <p>Soyisim: '.$lastname.'</p>
            <p>E-posta: '.$email.'</p>
            <p>Şirket: '.$company.'</p>
        </body>
    </html>
';