I am no expert, but I think it depends on which list your blacklisted for. Different lists look for different things. Their main function is to block spam, so a common cause is a infected email client on your network being used to send spam. If you have a Dynamic IP and it recently changed it may have been something with the previous owner of the IP. I think in my case, SORBS is blacklisting wide blocks of IP known to be used by residential customers and then tries to charge for delisting. To be honest though, I haven’t looked too much into it since I don’t use POP/IMAP for my email so not concerned about my blacklisting.
No worries. Thanks for getting back to me.