By default all IP addresses that get automatically blacklisted (because of protocol violations or some other type of attack/hacking attempt) are Temporary. This means that they will stay in the blacklist for an amount of time that you have defined in the Configuration Manager and then they will be automatically removed from the blacklist and allowed to connect again.
But Syncplify.me Server! also supports Permanent bans. The image here below shows how to turn a Temporary ban into a Permanent one.