Blocklists for 1.1.1.1.

A blocklist (DNSBL) is published in DNS. To ask about 203.0.113.7, a mail server looks up 7.113.0.203.bl.example.net: an answer such as 127.0.0.2 means listed, "no such name" means not listed. Domain lists work the same way with the domain in front. Before trusting a list, Hivex asks it about its own test entries, so a list that has shut down or blocks the lookup shows as "could not check", never as clean.

• The address your mail is sent from matters most. Find it in the headers of a message you sent, in the first Received line added by the receiving server; the email header analyzer shows it.
• Typing a domain checks the domain itself on domain lists, and its incoming mail servers' addresses on IP lists.
• Mail services (Gmail, Microsoft 365, newsletter platforms) send from shared addresses they look after themselves; a listing there is theirs to fix.

• Stop the cause first: a hacked mailbox or website form, an infected device, or a mailing list with addresses that never signed up. Otherwise the listing comes back.
• Then open each list's page from the result. Many lists drop an address on their own after a few days without spam; others need a request.
• A listing affects only the mail servers that use that list. Spamhaus, the one many large providers use, has its own free lookup.