PHP script error correction. Malformed header error.

I have an older PHP script that works just fine. It has recently started giving me an internal server error when someone registers on the site with an invalid email address. When you submit the form, the server pauses and then leads you to the "Internal Server Error" message. The information is still passed to the database and the user can click the back button and log in just fine. I need to stop the server error. Here is what I see in the error log: malformed header from script. Bad header=/home/site/dead.letter... I need this fixed today! I can only copy the portion of the script below that processes the account register email. I believe that this is where the malformed header error is coming from. Please look through this and post your bid on this project. I will pay someone $25 right now to create a fix. Keep in mind, this script WORKS as long as someone inputs a VALID email address! It gives me the error when someone inputs a made up email address. # ----------------------------------------- # sends email to webmaster # telling new user registered # ----------------------------------------- $topic = "New user registered - $lastid"; mail($email2,$topic, "$lastid $user_fullname $user_email registered", "From: $email1\nReply-To: $email1\n" ); # ----------------------------------------- # sends email to customer telling them their # profile is active # change the below to modify the email # ----------------------------------------- mail($user_email,"*Your Account is now Active*", " Thank you for registering with our site! ", "From: $email2\nReply-To: $email2\n" ); include("[login to view URL]"); echo "<font face=verdana, arial size=2>Your account is now active.<br><br><a href=[login to view URL]>Click here to login</a>."; include("[login to view URL]"); exit; };