Sending campaign to those that did not confirm subscription

Hi all,

I cannot seem to find a solid answer, both here in the forums or elsewhere. What is the legality regarding sending a follow-up message to those that did not complete the double opt-in? We have a very large segment of folks that did not complete their double opt-in, for whatever reason, and we would hate to miss out on that potential revenue. We currently have a sign-up form set up to encourage subscribing again to those that did not complete the double opt-in, but we’d like something that captures more people if possible. Could we send them a one time campaign asking for them to confirm, or to resubscribe? From my understanding that would then be considered spam, right, because we’d be messaging them when they weren’t subscribed? 
 

Thank you for any help!

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