Squirrel Mail or other Mail program via php?

I am able to use a php script to allow my users to send email.
What I am trying to do is to set up squirrelmail or roundcube.
So far I have had no joy.
Is that possible, or is it security disabled?
If anyone has tips or ideas about setting up roundcube or squirrel mail (squirrel is what I would rather use) please tell me. I think it requires server accesss and might be impossible. Or is it possible, but I am dumb? ;)
Thanks! <3 altervista!

They are IMAP clients, you can't use them on AlterVista since only HTTP(S) external connections are allowed.

Thank you for your answer, I really appreciate your effort, since it saved me some time! Can I ask? Are any of pop3 mapi or exchange possible ways to implement a webmail service through altervista?

You would need to use an external service to do that. On AlterVista you can't setup a mailbox service.

Ok, thank you.