If your setting your mail to header correctly, and your mail from correctly then it's likely your mail server is re-writing it.
I had a similar issue sometime ago where postfix was rewriting headers containing my external domain name, to my local domain name, so when people where replying the mail was failing, unless it was sent inside the network.
Looking at your header construction, you might want to write the last two lines like this:
$headers = "MIME-Version: 1.0\r\n";
$headers .= "Content-type: text/html; charset=iso-8859-1\r\n";
$headers .= "From: WEBSITE.COM USER <" . $row2[pmail] . ">\r\n";
$headers .= "Reply-To: WEBSITE.COM USER <" . $row2[pmail] . ">\r\n";
I've always had problems in the past putting array literals directly into strings, and have found i'ts always better to concatenate them using the . operator instead.
I would also check your [pmail] part. if this is a variable name then it should be [$pmail] , if this is a static identifier then it should be ['pmail']
Cheers
Shawty