Our server hosts this customers domain name, but the content is hosted on someone elses shared web server. The problem is that they have all this crazy security and fire walls. They told me that their system requires the IP address and the domain name to access the content on their server.... Mind you not the account name. The server somehow decifers the ip and compares that to the domain before allowing access.
Just to give you an idea of the security. There is a lot of security... the only way in to acces files or edit files on their system is over ssh and you jump threw 3 different ips and fire walls.