Trouble with mail() on aol emails

[refiking]

So, I have a simple email function that works for every email except aol, which makes no sense to me.  What do I need to change to make sure it works with EVERY email carrier?  Here's my current code:

 

function sendemail ($to, $from, $subject, $message){
$headers = "From: " . $from . "\r\n";
$headers .= "Reply-To: ". $from . "\r\n";
$headers .= "MIME-Version: 1.0\r\n";
$headers .= "Content-Type: text/html; charset=ISO-8859-1\r\n";
mail( $to, $subject, $message, $headers );
}

 

P.S.  I also tried to just remove the headers and that still didn't send the email to the aol accounts.

[trq]

Is the From header being set to a valid email address on your domain?