[kh99]

I think that might be the default for new subscriptions, but each subscription can have a different type, so I think you'd need to update the various subscription tables and change the type (looks like the field is 'emailupdate' in most of them).

Someone else was asking the other day about a similar issue (disabling emails that bounced) and came up with the idea of simply deleting the email from the user table. I can't say exactly what would happen if you did that, but it does look like the emailing function won't try to send out an email if the "to" address is blank.