there is a setting in each Client record that can disable email for them. one sec... yep here it is:
Block WHD E-Mail to Client
If checked, e-mail intended for this Client will be blocked, regardless of the e-mail settings on Tickets that might be assigned to that Client, etc.
Hmmm.. but if you want to turn it off just for certain *actions* for that client and not for all mail to that client.... i'm not sure that that is possible. perhaps in that case you could set up a server side rule on your mailbox to drop mails for that email account with particular subjects?
I'd rather it not respond at all, than keep opening close tickets so this will be perfect.