I am a brand new list owner and request assistance in figuring out why some folk subscribing to our list receive the e-mail asking them to confirm their intent to subscribe to the list by responding OK and others do not.

Our header is set to Subscription=Open.
It has never been set to Subscription=Open, Confirm
Without the "Confirm" I expected that potential subscribers would not receive the e-mail asking them to confirm their intent to subscribe to the list.

Yesterday afternoon I watched 5 different people subscribe.  4 got no confirmation e-mail; 1 got the confirmation e-mail.

Is there another keyword in the header than might be complicating things or some setting on the list server or something else going on?