Domain lists and IP lists are not the same thing
Most blocklists are keyed to the sending IP address, not the domain, and a domain's sending IP cannot be read from DNS because it depends on your provider. So a domain-only check (Spamhaus DBL, SURBL) tells you about domain reputation, while catching an IP listing (Spamhaus ZEN, Barracuda, SpamCop) requires you to enter the IP your mail actually sends from. We check what we can from the domain and ask for the IP for the rest, rather than pretending a clean domain means a clean IP.
What to do if you are listed
A listing sends your mail to spam regardless of how clean your records are, so it is the first thing to fix. Find the cause, a compromised account, spammy content, or a bad list you sent to, correct it, then request delisting on each list's own website. Delisting only sticks if the underlying reason is gone, so fix first and request second.