Add bold text in mail sender text

Here is the code:

$email_body = "You have received a new message. ".
    " Here are the details:\n\n Name: $name \n Email: $email_address \n Message \n $message";

I want to add bold text to: "Name:", "Email:", and "Message"

I have tried using the "< b > name: < /b>" (without space of course), but it doesn´t work. I want the text to be bold when i receive the mail.