Q: Does the Store & Forward feature mean that you're storing my mail for 15 days?
A: Our Store & Forward feature for disaster recovery is set to a 15-day lifecycle and is only activated by a server outage on your end. We only store mail for reattempted delivery if your server is down. As soon as it's back up and we can deliver the queued mail, we erase it on our side.
A: S/MIME would be handled by your own servers and/or clients.