Blocklist

A blocklist lists IP addresses or domains associated with spam, malware or abusive sending. Most are published as DNSBLs (RFC 5782): a mail server checks a connecting IP by reversing its octets and looking it up under the list's DNS zone, so 192.0.2.10 becomes a query for 10.2.0.192.zone. A returned 127.0.0.x answer means 'listed', and the specific value indicates which list or reason.

There are IP lists (for example compromised machines, known spam sources, or address ranges that shouldn't send mail directly) and domain lists, which are checked against sender domains and the domains of links in a message. Spamhaus is one of the most widely used operators; each operator has its own listing criteria and removal process.

A listing can cause outright rejections (often a 5.7.1 SMTP reply that names the list) at every receiver using that list. Typical triggers in outreach are hitting spam traps, sending to old or guessed addresses, sudden volume spikes and complaints. Removal usually requires fixing the cause first; asking for delisting while the behaviour continues rarely works.

Skrap.ai doesn't monitor or remove blocklist listings. It helps with a common cause: sending to addresses that don't exist. Verify lists with the free email verifier before each campaign so you're not mailing stale, guessed or abandoned addresses.