DNSRBL uses intelligent filters that constantly sample incoming mail feeds to determine if a mail violates DNSRBL policies (Junk Mail). DNSRBL does not soley rely on spam traps.
A valid SPF record is recommended. Double check that your SPF record(s) are valid.
Mail servers should have an RFC compliant host-name; a-record, valid PTR record and MX record.
Shared email servers may be listed due to no fault of your own. We try not to list shared email providers like Gmail and Yahoo that host a large amount of end users.
In any case you may wish to discuss any listing issues with your email provider.