A user is attempting to connect to a remote server via SSH and receives the following message:

The authenticity of host ‘mail.example.com (208.77.188.166)’ can’t be established.
RSA key fingerprint is 92:32:55:e9:c4:20:ae:1b:2c:d7:91:40:90:89:1c:ad.
Are you sure you want to continue connecting (yes/no)?

What does this indicate?