Hi, @Dean Loudermilk ,
For the part
send something to a third party outside my organization so that person can upload documents securely?
Are you holding the confidential documents now in SharePoint library and want to send them to a external user? And the user need to upload them to a different site? As long as the documents are held in SharePoint, SharePoint and OneDrive safeguard your data in the cloud. And we have external sharing feature available for you to enable external users have an access to these contents inside SharePoint, which is also protected by Microsoft.
According to your description, it seems your customer or you are using SharePoint and needs to send documents outside SharePoint for uploading. As I am not sure the whole process and actual requirements, not much I can say about a best practice. It may be better to open a service request or ask for a SharePoint consultant to get a whole solution for your scenario.
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