We send legitimate e-mails to our opted-in customers in bulk. Recently we started having issues with our IP reputation, which we are working on to improve. We are digging into the issue to find the root cause and would like to know from where does various RBLs and DNSBLs collect data from? For example, I read from SORBS FAQ that they have a set of 'feeder servers' from which data is collected.
Are these feeder servers the mailservers of various reputed email service providers like Gmail or Hotmail?
From SORBSs' website:
6: What and where are the feeder servers..?
The 'feeder' servers are a selection of servers that send addresses of selected the incoming connections to the SORBS servers for testing. The list of feeder servers will not be disclosed, by request of those server administrators.
I am not looking for an answer to the things we should do to keep us away from the list, but trying to find out how these RBLs/DNSBLs collect the info.