553 5.7.1 [BL21] Connections will not be accepted from IP because the IP is in Spamhaus's list
Yahoo refused the connection because the sending IP is on a Spamhaus list. BL21 names Spamhaus specifically; BL23 is Yahoo's own blocklist with the wording "Connections not accepted from IP addresses on Spamhaus PBL". Until the listing is removed, every message from that IP to Yahoo or AOL bounces at connect time.
What the server replies
553 5.7.1 [BL21] Connections will not be accepted from 203.0.113.10, because the ip is in Spamhaus's list; see https://postmaster.yahooinc.com/error-codes
- Sent by
- Yahoo and AOL
- Type
- PermanentRetry fails
- About
- Reputation and blocklists
- Enhanced code
- 5.7.1
Who sends it
Yahoo and AOL inbound servers at connection, before the session begins. The bracketed BL code tells you which list; the PBL variant means the IP is in a range Spamhaus has marked as not for direct mail (home broadband, dynamic cloud ranges).
Why it happens
- The IP sent spam, or a machine behind it is infected, and Spamhaus listed it on SBL or XBL.
- The IP is in a residential or dynamic range on the Spamhaus PBL.
- The IP belongs to a hosting range with a bad track record.
- The IP is clean but shares a /24 with a spammer and the listing covers the block.
How to fix it
Check the listing
Enter the IP at check.spamhaus.org. The result names the list and the reason, and for XBL and SBL listings what evidence Spamhaus has.
For PBL, relay instead
PBL listings are about the range, not your behaviour, and cannot be removed for a residential or dynamic IP. Send through your ISP's or a provider's SMTP relay.
For SBL or XBL, fix then request removal
Clean the infected host or shut off the abusive sender, then request delisting on the Spamhaus page. Removal usually takes effect within an hour, and Yahoo picks it up on its next lookup.
Confirm with a test
Once delisted, send one message to a Yahoo address you own before resuming the queue.
Check it yourself
These free tools show the records and connections behind this code for your own domain or server.
Related codes
- 550 5.7.1 Service unavailable, Client host blocked using Spamhaus (S3140, S3150)Microsoft refused the connection because the sending IP is on a blocklist.
- 554 5.7.1 Service unavailable; Client host blocked using zen.spamhaus.orgThe receiving server checked your IP against a DNS blocklist and found it listed.
- 550 5.7.606 Access denied, banned sending IPThe sending IP is on Microsoft's blocklist for Microsoft 365 recipients.
Sources
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