It's not up to Perl or 'CGI' to know what to do if a message is undeliverable. After all, once the message has flied through your method of sending (you don't specify: Perl module? If so, which one?) it's at the hand of the demon handling the sending of your mail.

So basically, you need to look at the config of your sendmail program on your server and see what this is set to do. You can usually specify a return to address, or to delete bounced messages and you can also specify how long the program should try before giving up.

The best you can do with your Perl/CGI script is to make sure that you set a correct From: and/or a Reply-To: address in your message headers, so that if the sending process fails your sendmail demon will be able to send you a message explaining why.

Hope this helps.

- wil