How can I include a files contents in mail body?

I understand how to send mail , from the manual,
<?
$mailTo = "[email protected]";
$msgSubject = "Pretty Cool.";
$xHeaders = "From: [email protected]\nX-Mailer: PHP/".phpversion();
$message = " Now is the time for all good men to come to the aid of the
party";
mail($mailTo, $msgSubject, $message, $xHeaders);
?>

But, I have a file created by another scrip... living in
"/includes/a_file_created_with_html_code_in_it.txt"

How can I get the contents of that file into the $message variable so it
becomes the actual message body?

I've tried all sorts of ways to 'include' it, but to no avail.
Could some knowledgeable soul point me in the right direction please?

Thanks so much
Robert
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