1. Can I use FTPS
   

Unix

1. Can I use FTPS
   
2. Do I need to use implicit or explicit?
   
3. Is FTPS slower then normal FTP?
   
4. Can the customer use SFTP?
   
5. Can FTPS work on a NAT'd or firewalled connection?
   

Windows

Unix

2. Do I need to use implicit or explicit?
Explicit

3. Is FTPS slower then normal FTP?
Yes. Data is being encrypted, so there is more data being sent and you have to allow for time to encrypt and unencrypt the data.

4. Can the customer use SFTP?
No SFTP is FTP over SSH
SSH access is not allowed on RCN's servers

5. Can FTPS work on a NAT'd or firewalled connection?
The short answer is that FTPS and firewalls (and devices performing NAT) do not interact well. The control connection happens on a well-known port, and has no issues; it is the data connection that poses problems for FTP-aware firewalls. In a non-FTPS session, the firewall can inspect the FTP server's responses on the control connection to a client's PASV or PORT command, and thus know which on which ports/addresses the data connection will be established. In an FTPS session, though, those control connection messages are encrypted (that is the point of using FTPS, right?), and so the FTP-aware firewall cannot peek. Hence, it cannot know which on which ports the data connection will be established. For firewalls that are configured to always allow a certain range of ports (such as might be configured using the PassivePorts directive), FTPS should function without issue.