Email blocklists, checked and fixed

Spamhaus lists sending IPs and domains with a bad reputation, and a large share of mail servers query it, so a listing blocks delivery widely. Check your IP against the zen.spamhaus.org zone (or your domain against dbl.spamhaus.org), stop whatever caused it, then remove the listing at check.spamhaus.org. Removal is always free.

Includes: ZEN, SBL, CSS, XBL, PBL, DBL

The Barracuda Reputation Block List (BRBL) lists sending IP addresses seen emitting spam, and Barracuda appliances plus many mail servers query the b.barracudacentral.org zone to reject them. Check the IP your mail leaves from, stop whatever caused the listing, then submit Barracuda's removal-request form. Barracuda says a valid request is typically processed within 12 hours.

Includes: BRBL, Barracuda blacklist, b.barracudacentral.org, Barracuda Reputation System, Barracuda Central

SpamCop runs the SCBL, a list of sending IPs that transmitted mail reported as spam by its users and spamtraps. Most mail servers query bl.spamcop.net, so a listing blocks delivery widely. There is no removal form: stop whatever is sending reported mail, and the listing expires automatically about 24 hours after the last report.

Includes: SCBL, SpamCop Blocking List, bl.spamcop.net

UCEPROTECT runs three IP blocklists: Level 1 (dnsbl-1.uceprotect.net) lists your individual sending IP, Level 2 lists that IP's whole netblock, and Level 3 lists your provider's entire ASN. Every listing expires free seven days after the last detected abuse, so stop the spam, authenticate your mail, and you clear without paying.

Includes: UCEPROTECT-Network, UCEPROTECTL1, UCEPROTECTL2, UCEPROTECTL3, dnsbl-1.uceprotect.net, dnsbl-2.uceprotect.net, dnsbl-3.uceprotect.net

Invaluement is a commercial anti-spam service that runs three DNS blocklists: ivmSIP and ivmSIP/24 list spam-sending IP addresses and subnets, and ivmURI lists spammy domains found in email links. Mail filters subscribe to it as a Spamhaus supplement, so a listing blocks your delivery at the receivers that use it.

Includes: ivmSIP, ivmSIP/24, ivmURI, invaluementSIP, invaluementURI, IVM

Cloudmark Sender Intelligence (CSI) is an IP reputation service, not a blacklist: Cloudmark scores your sending IP and its customers (mail providers) decide whether to reject you. If a bounce cites CSI, stop the spam, fix reverse DNS and authentication, then submit the reset request at csi.cloudmark.com/en/reset. Cloudmark publishes no fixed removal time.

Includes: CSI, CSI Global, Cloudmark CSI, CSI-Global, Cloudmark

Your sending IP gets blacklisted when receivers or spam traps see abuse tied to it: a compromised mailbox or host sending spam, an open relay, spam complaints, or a spammy neighbor on shared or snowshoe IP space. Missing reverse DNS and unauthenticated mail (weak SPF, DKIM, DMARC) make listings far easier to earn.

Includes: blacklist, blocklist, DNSBL, RBL, IP reputation

Backscatter is misdirected bounce mail: your server accepts a message, then sends a non-delivery report to a forged sender who never wrote to you. Backscatterer.org (ips.backscatterer.org, run by the UCEPROTECT-Network) lists IPs that do this for four weeks. The fix is to reject invalid recipients during the SMTP session, not bounce them afterward.

Includes: Backscatterer, ips.backscatterer.org, UCEPROTECT Backscatterer, email backscatter

An email blacklist (also called a blocklist or RBL) is a published list of IP addresses or domains with a bad sending reputation that receiving mail servers check in real time to reject, defer, or flag your messages. The ones worth watching: Spamhaus, Barracuda, SpamCop, UCEPROTECT, Cloudmark CSI, invaluement, SURBL, URIBL, and Backscatterer.

Includes: email blacklist, email blacklists, RBL, DNSBL, realtime blackhole list, email blocklist directory

An MxToolbox blacklist check scans your sending IP or domain against 100+ DNS blocklists and marks each one pass or listed. Most of those lists barely affect delivery: only a few, chiefly Spamhaus, Cloudmark CSI, and Barracuda, are widely enforced. Read the result by that lens, then fix the cause with authentication instead of chasing every red row.

Includes: MxToolbox blacklist check, MXToolbox blacklist check, MxToolbox RBL check, MxToolbox blacklist lookup, mxtoolbox blacklists