Our application suite includes a procurement platform that transmits purchase orders via FTP to dozens of vendors. Until now, this application has run on one server so these FTP transmissions have originated from one IP address. Over the years many vendors have white-listed this one IP address on their internal networks. Our infrastructure is growing and we need to host this aspect of our application on more than one server and therefore FTP transmissions would be sent to these vendors from new IP addresses. Our fear is that if we make this move, transmissions will begin to fail as transmissions are denied by the vendors' firewalls, etc. If possible, we would like to avoid coordinating this sort of move with each vendor due to the number of vendors and varying reliability of their IT resources.
We are currently researching FTP proxying, but I was wondering what other options we may have. I'm sure there are other SaaS shops our there that have come across similar issues and I would love to hear how they've approached them.