Hi Marianne,
Yes, you can still install ListMail. Email forwarding to script is entirely optional but is required for signup-by-email and on-the-fly bounce processing.
DetailsSignup-by-email is not required - most of my users prefer to use a standard signup form for accepting subscribers. (List Settings -> Signup Code)
There is an alternative bounce-handling method that utilizes a standard mailbox which is processed daily.
DetailsPlease let me know if I can be of further assistance!
Regards