Yahoo 553 5.7.1 [BL21]: “connections will not be accepted … ip is in Spamhaus's list”

Short answer: Yahoo refuses connections from your IP because it is on a Spamhaus blocklist. Find out why the IP was listed, fix it, and request removal from Spamhaus. Yahoo starts accepting mail again once the listing is gone.

The bounce looks like this
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

What it means

A 553 code is permanent: Yahoo won't take mail from that IP at all while the listing lasts, and retrying does not help. Yahoo checks Spamhaus, which lists IPs that send spam, are infected, or sit in ranges that should not send mail directly (typical for home connections and some cloud ranges).

How to fix it

  1. Look up the IP from the bounce on the Spamhaus IP and Domain Reputation Checker; it says which list and why.
  2. Fix the reason first: a compromised mailbox, an infected PC on the network, an open relay, a website form or script sending spam.
  3. Then follow the removal link Spamhaus shows for that listing. Policy lists for dynamic or cloud ranges usually mean you should send through your provider's mail server or a sending service instead.
  4. On a VPS, make sure the reverse DNS is set to your mail host name and only your own mail software can send.
  5. While you wait, a reputable sending service (your mailbox provider's SMTP or a transactional email service) gets mail out without the listed IP.

Check your domain now

After the fix, send a test email to see SPF, DKIM and DMARC pass on a real message, then keep an eye on it: free DMARC monitoring shows every service that sends mail as your domain and which ones fail, in plain English.

Rather not touch DNS? I set up SPF, DKIM and DMARC without breaking your other senders, with a before/after report.

Get it fixed on Fiverr

Prefer to do it yourself? Get the step-by-step Fix Kit ($15) – 28-page guide, checklist, 20+ providers.

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