We see that a lot of subscribers from our current email list also use
the campaign we started with upviral. They subscribe (while they already did in
the past) and receive a reward. Once their email address is known in Upviral
this is not possible anymore. Would be great if is't possible to upload these existing
subscribers to upviral so they cannot receive the reward anymore. Or if another solution could be build to prevent us from rewarding existing subscribers.