Your ip has been blacklisted, try accessing the server for another IP address. When you gain access your can remove the IP address within the blacklist settings
If the server is remote for your machine , you need to try from another machine which has a different wan IP address
The blacklist does get removed after a certain time but can not rember what the time delay is
If you can not access the server because you have forgotten your password, and using the 15.5 sp6 type your username and password incorrect 3 times and you should get an option to reset the password. This does mean that you have setup smtp correct and added an administrator email address