My clients on my network could access FTP servers behind our ISA 06 firewall but they could not create or delete anything on that FTP. I checked to make sure the permissions on the FTP were setup correctly. I narrowed it down to ISA blocking Incoming FTP traffic coming back from the FTP servers. I did some searching and there are many issues out on this. Others issues vary slightly but I did find something that worked for me. I setup the below rule on ISA.
ISA FTP rule:
- Action: Allow
- Protocols: FTP (21 TCP Outbound /FTP Filter Disabled) – FTP Server (21 TCP Inbound /FTP Filter enabled)
- From/Listener: Internal
- To: External
- Condition: All Users
I hope the above ISA rule is useful for someone else as well. Here is some more useful information when Troubleshooting Outbound FTP Access in ISA Server: http://technet.microsoft.com/en-us/library/bb794745.aspx