Security checks you can run yourself: headers and IP lists

• Security headers. Request the page and read the protective headers in the response, with curl -I or in the browser's network panel: what is present, what is missing, and what each one is for. The rules behind them are covered under rules.
• Address reputation. Reputation services publish what they have observed from an address. That record is the input behind most reputation-based decisions, not a verdict about the address itself. Paired with IP reputation.
• Blocklist check. A narrower question: whether an address appears on public lists. Each list answers for itself, through a lookup its operator publishes. That is a different question from reputation, and the two are worth keeping apart, because presence on a list is a fact while reputation is an interpretation.
• Botnet association. Threat-intelligence feeds record addresses tied to known automated networks, explained under botnets. Worth checking when a pattern in your logs comes from somewhere you do not recognise and you need to know whether it deserves a closer look.
• Firewall in the path. Response headers, cookies set on first contact, and the page returned for a refused request usually show whether a site sits behind a filtering layer. Useful mostly when inheriting infrastructure nobody documented, where the first question is what is already in the path.

Start from the symptom rather than from the list.

Visitors or partners say they are refused. Read what the refusal says first: a 403 Forbidden and a 429 Too Many Requests point to different causes. Then check whether their address is listed, since a shared or recycled address can carry somebody else's history.

Mail from your server bounces, or a service rejects your calls. Run the blocklist check on your own address before changing anything else; a listing explains both symptoms and has a published removal route.

You are preparing a launch or an audit. Read your security headers. The simple ones take minutes to add; Content Security Policy takes longer and is worth starting in report-only form.

An unfamiliar pattern shows up in your logs. Check the addresses against reputation and botnet sources before blocking anything. Many people can share one address, and how to block without catching them is covered under IP blocking.

Headers change whenever someone changes the server, the application or anything in front of them, so read them again after each such change rather than on a calendar. A header that disappeared in a deployment is invisible until someone looks.

Lists and reputation records change daily. Check addresses you send from, such as a mail server, on a schedule; check other people's addresses only when a decision depends on the answer, and look again before acting on an old result.

One thing is missing on purpose.

There is no attack test. A tool that generates load against a site you name is indistinguishable from the thing it claims to help you defend against, and running one against infrastructure you do not own is not ours to offer. Testing resilience is a legitimate need and belongs in an arrangement where both sides know it is happening, not behind a button on a public page.

What these checks do instead is describe what is observable: what a site returns, what is published about an address, and what a pattern resembles. Deciding what to do about it is covered under operations.