Seeking Technology To Upload Files From Public Internet To Intranet

Currently our external customer submit all other data through our public web site, but submit some artifacts (.coc, pdf...) through email, then our administrators save those files come from email to our internal server. This is not efficient, because we cannot identify immdeately if our customer submitted their required documents before our administrator saved them to the server. I am seeking a technology that external customer can upload files through the public website toan intranet server that the external customer would not notice they are accessing intranet server.