I believe you are thinking of being on a mailing list where you can simply hit "unsubscribe" and be done after you confirm the action.
IPCT is not a mailing list, it is a discussion forum.
Receiving emails from IPCT will not happen until you first create a user account, login, then post to or follow (aka watch) discussion threads as said user. As this thread is your first ever post, you obviously have voluntarily chosen to watch threads over time which, in turn, notifies you via email when the thread(s) have new activity.
In order to "unwatch" a thread, you are required to login so the message board software can track which threads your username is watching. This is how most systems provide the customized content of your choosing. FYI, the "unwatch" button is located at the top right of the respective thread you have previously contributed to or chosen to "watch".