Thanks for the feature request!!! This will be a nice feature which will enhance Schedule-One-Off of MassMailer.
I will keep you posted once this will gets implemented.
Mansa Support Team
I have used your Schedule-One-Off of MassMailer and i am pretty much comfortable with this feature. You guys did an excellent job in order to build this functionality. Here, i would like to ask you guys can we display an appropriate message on the resulting screen when an Invalid Lead ( or Contact ) or Email-opt-out field is checked?