Unfortunately the feature to resend an email, to all of your unopens, will not be available to users who do not pay for unlimited sending. In other words, if you’ve obtained free unlimited sending, this option will not be available.
By doing this, we remove the possibility of abuse of this system. The possibility to resend to unopens in an unlimited capacity could lead to damage to the reputation of our servers in which we cannot allow. We apologize for the inconvenience.