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Yahoo [BL21]: IP is on a Spamhaus blocklist

553 5.7.1 [BL21]Connection refused because the IP is on a Spamhaus listPermanent: retrying will not helpFrom Yahoo Mail and AOL

Typical wording
553 5.7.1 [BL21] Connections will not be accepted from 203.0.113.100, because the ip is in Spamhaus’s list

What it means

Yahoo consults Spamhaus blocklists when a server connects. A BL21 response means the connecting IP was found on one of them, so Yahoo refuses mail at the connection stage, before looking at any message. The text usually reads like the example and names the IP that was checked.

Yahoo is only the messenger here. Removing the listing at Spamhaus is the fix, and once that propagates Yahoo will accept connections again without any separate request. Other bracket codes in the BL family point to other lists, so read the code carefully.

Likely causes

  • The IP is listed on the Spamhaus SBL for spam sources or on the XBL/CSS for infected or misbehaving hosts.
  • The IP is in a range listed on the PBL, which marks dynamic or residential addresses that should not send mail directly.
  • Another customer on a shared hosting or cloud IP generated spam before you got the address.
  • Malware or a compromised account on your network is sending spam.

How to fix it

  1. Look up the IP from the bounce in the Spamhaus checker at check.spamhaus.org to see which list and why.
  2. Fix the cause the listing describes: clean infected machines, secure accounts, close open relays, set correct reverse DNS.
  3. For PBL listings on a home or dynamic IP, send through your provider’s relay or a mail service instead of directly.
  4. Request removal through the Spamhaus checker once the cause is fixed, then retry your queue.

Checks that apply

  • Blacklist Check Checks the IP against Spamhaus zones and dozens of other DNSBLs at once.
  • Reverse DNS (PTR) Missing or generic reverse DNS is a frequent factor in CSS and PBL listings.
  • ASN Lookup Identifies whether the IP belongs to a residential or hosting network, which matters for PBL.
See the example diagnosed

The classification runs without network lookups and we never store your paste.

FAQ

Do I need to contact Yahoo after delisting?
No. Yahoo checks Spamhaus live, so once the listing is gone, connections are accepted again.
How fast is Spamhaus delisting?
Self-service removals for XBL, CSS, and PBL usually take effect within hours. SBL listings are handled by Spamhaus staff and can take longer.

Yahoo Sender Hub

All 191 bounce codes