What is S5H?
Still have a question, spotted an error, or have a better explanation or a source we should cite?
all.s5h.net checks IPs, IPv6 included. It is published on usenix.org.uk.
What the operator says
"a collated list of all sources and attack vectors" usenix.org.uk, RBL page, read 31 Oct 2026.
What it really measures
Anything that sent spam, in any form, to the site's own server addresses.
What to think about
We class this as low-impact, and it is one of the easier ones to clear, so make sure the cause is gone first.
How to get off it
Open the removal page from the listed IP itself, and you are delisted at once. More than 3 requests a day from one IP gets it blocked from removing itself. If that fails, the site's form asks for proof you dealt with the security problem. That route is slower.
What "low-impact" means on these pages: the big mailbox providers rarely use the list, so it rarely affects delivery at Gmail, Outlook or Yahoo. It can still point at something worth fixing.
Want a hand getting this delisted? Here is how to write to a list's operator, or ask a person on our free SOS Hotline. Tell us the list and the IP or domain, and we reply within 48 to 72 hours.
A separate job: cleaning your list does not remove a listing. If you also want to know who on your list is safe to send to, clean your first 1,000 free.
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