On most support calls related to SFTP, the root cause is a customer or customer counterparty's corporate or network firewall.

SFTP is very commonly blocked by firewalls, and often firewall changes can introduce new issues that didn't previously exist.

Manually Whitelisted IP Addresses

Have you manually whitelisted any IP addresses anywhere? If so, you need to all of the appropriate IPs are whitelisted, not just some of them.

If your site uses a custom domain, you have two dedicated IPs that need to be whitelisted in your firewall. You can find your dedicated IPs on the Firewall page of your site. If you have a custom domain, you also need to ensure that you are connecting to it, and not to [your_subdomain].files.com.

If you do not have a custom domain, ensure that our all of IPs on this list are whitelisted, not just some of them. There are quite a lot of IPs on that list and you need to whitelist all IPs or else you will experience failures. If whitelisting that many IP addresses is a problem for you, the solution is to move to a custom domain. This will get you a pair of IP addresses you can whitelist (see the prior paragraph.)

Consider An IP Whitelist

If you have not whitelisted IP addresses, maybe your firewall administrator requires an explicit whitelist for SFTP traffic. Please submit a request to your network or firewall administrator to allow SFTP port 22 traffic to all of the IPs on this list. If your firewall team does not allow whitelisting port 22 traffic, ask for port 3022 instead and see the next paragraph.

Try Other Ports

By default, SFTP is used on port 22. Files.com also supports 3022 as an alternate port. Many firewalls will allow traffic on port 3022 despite blocking it on port 22. We recommend testing this next if you have exhausted other firewall issues. In many cases, simply using the alternate port will get your corporate firewall to let the connection through.