553 5.7.1 [BL21] error (Yahoo / AOL): Connection refused, IP is on a blocklist
Yahoo refused the connection because the sending IP is listed in a DNS blocklist it uses.
How to fix 553 5.7.1 [BL21]
- Check the IP on the Blacklist Checker and follow the listing's removal steps.
- Find out why it was listed before requesting removal.
Why this happens
Receivers score every sending IP and domain. A history of complaints, spam-trap hits, high bounce rates or a listing on a blocklist pushes that score down until mail is deferred or refused outright.
How to keep it from coming back
Warm up new domains and IPs gradually, send only to verified and relevant recipients, keep complaints near zero, and check your IPs and domains on blocklists regularly. Spread volume across mailboxes and domains instead of pushing one harder.
Should I retry a 553 5.7.1 [BL21] error?
Not as it stands. A permanent error means the same message will be refused again until the cause is fixed on your side. Fix the cause first, then send a fresh message; if it keeps failing after that, check the full text of the bounce for the exact reason.
Got the full bounce message?
The text after the code names the exact reason, and the same code can mean different things at different receivers. Paste the whole message into the decoder - it runs in your browser and nothing is sent.
Open the bounce decoderRelated error codes
Seeing this again and again? That's usually a reputation or authentication problem we can trace and fix at the source.
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