Confirmation email caught by spam filter

hi, I use the following code (from php.net) to send confirmation email to the person that just created an account:

 $headers =    "MIME-Versin: 1.0\n" .
                "Content-type: text/plain; charset=ISO-8859-1; format=flowed\n" .
                "Content-Transfer-Encoding: 8bit\n" .
                "Reply-To: Orders <lamp@afan.net>\n".
                "From: Orders <orders@mydomain.com>\n" .
                "X-Mailer: PHP" . phpversion();           mail($to, $subject, $body, $headers);

$subject is something like "[MyDomain] Your new account", and $body is just few plain text details about person who created the form. The same code I use to reset a password: a visitor enters his/her email address and the link with session ID is sent to entered email address. The problem is the confirmation emails and "reset password" emails are very often caught by email filter and finish in Spam/Junk folder, or even stopped by ISP. What am I doing wrong, or what to do to improve the code? Also, how can I get bounced emails? Thanks, Afan