Unsubscribing a list of emails

I'm setting up e-newsletter on a site and the client has two csv spreadsheets - one for valid existing subscribers, the other is their suppression/opt-out list.

I have successfully imported the valid list, but I can't figure out the best way to handle the suppression list. Was thinking perhaps import to a separate group, then unsubscribe the GROUP from all mailings?

Thanks for your help...