I don't like this method too much. Mainly because from a personal mail server I can send a mail with "From:" equal any mail if I want, so with this method I could subscribe and confirm any user I want, and I think this is not a very good practice.

The thing with bounced e-mails is that an valid working e-mail can still bounce due to a error such as full mailbox. If the e-mail does bounce, is there anyway I can make my perl script notify the subscriber through html?

It depends on the configuration of the remote mailserver. Maybe it's throwing 4xx error when user mailbox is full and 5xx when user doesn't exist, or maybe it's accepting anything and sending DSNs, or maybe... I think you shoul only send the mail, and then the user should worry about why it didn't got delivered.