Dear Vasilis,

The list administration page is at
  https://sympa.inria.fr/sympa/info/caml-list
with an "unsubscribe" page:
  https://sympa.inria.fr/sympa/signoff/caml-list

(I'm assuming that you want to unsubscribe from the  caml-list@inria.fr mailing-list, not from discuss.ocaml.org )