The server's certificate is unknown. Please carefully examine the certificate to make sure the server can be trusted.

[daryl.hill]

We are currently using FileZilla 3.26.2 to connect to one of our FTP sites, and we get the error "The server's certificate is unknown. Please carefully examine the certificate to make sure the server can be trusted." The encryption setting is the default "Use explict FTP over TLS if available", if we use "Only use plain FTP (insecure)" it works without throwing up the certificate error.

Now the interesting thing is, if we use something like FireFTP and use the security setting "Auth SSL (Better)", which I believe uses the same protocols as FileZilla's "Use explict FTP over TLS if available", we don't get any certificate errors at all and it connects straight away.

Is there anyway to get round this problem with FileZilla at all?

[boco]

It is neither an error nor a problem. FileZilla just doesn't use the OS certificate store (which might become compromised), instead, it follows the TOFU model (TOFU = Trust On First Use).

That means, at least upon first contact to every new server, you will get that popup, to carefully check and verify the certificate. If you trust it, click the button (+check the box for permanent trust). With permanent trust, you won't be bothered again for that exact certificate until it expires.