Inclusion in the PSBL indicates the following: If you are running your own mail server, that server/IP address was used to send spam, either via an open-relay or someone hijacking an account on the server to send spam. In this respect, if the issue is corrected, your IP address will most likely eventually time out and be removed from the list unless you manually request delisting. There is also the possibility that you were hit with a Trojan or "zombie" caused by malware, which, if not quickly resolved, could result in a long-term listing in the PSBL.