Hi Mark. I'd recommend taking a look at the bounce report and removing any bad addresses you see. If you recognize any addresses in there and don't think they should be bouncing, the emails may be getting blocked on their side. If that is the case, they should try safelisting your emails. If that does not work or if you have any other questions, feel free to give our deliverability department a call. You can find their number and hours of operation here.