<?php while ($users = $stmt->fetch(PDO::FETCH_ASSOC)) : ?>
    <p><?php echo $users['lastLogIn'];?> - <?php  echo $users['userName']; ?></p>
<?php endwhile; ?>

function send_mail($email,$message,$subject){
require_once('mailer/class.phpmailer.php');
$mail = new PHPMailer();
$mail->IsSMTP();
$mail->SMTPDebug  = 0;
$mail->SMTPAuth   = false;
$mail->SMTPSecure = "";
$mail->Host       = "10.10.10.10";
$mail->Port       = 25;
$mail->AddAddress($email);
$mail->Username="Anonymous";
$mail->Password="Anonymous";
$mail->SetFrom('noreply@email.co.uk','Hello');
$mail->AddReplyTo("noreply@email.co.uk","Hello");
$mail->Subject    = $subject;
$mail->MsgHTML($message);
$mail->Send();
}

$email = ("email@email.co.uk");
$message= "
    Hello, $email
   <br /><br />
   Please find a list of users below who logged in today :
   <br /><br />
   I want the while loop content here";
$subject = "Daile User Log";

send_mail($email,$message,$subject);