The S5H list, all.s5h.net, collects IPs that send spam to its honeypot addresses. Getting off it is about the fastest removal in the business.
Run one HTTP request from the listed IP itself, for example curl -4 http://www.usenix.org.uk/content/rblremove on that server. S5H delists the IP immediately. On a server with several addresses, make sure the request goes out from the listed one.
Use S5H's manual removal form with your email, the IP, why it was listed, and what you fixed. Replies can take a few days, and approved removals go through within 30 minutes.
If your IP hit S5H's honeypots once, it can again. Generator Labs checks your IPs against S5H and hundreds of other blacklists and alerts you by email, Slack, SMS, or webhook when a listing reappears. Free for your first host.
Yes.
Instant with the HTTP request; within 30 minutes of approval with the manual form.
Your IP sent spam to one of S5H's honeypot addresses.