554 5.7.1 / 550 5.7.1: Blocked using a blocklist (DNSBL)

AnySMTP

The error usually looks like this:

554 5.7.1 Service unavailable; Client host [x.x.x.x] blocked using zen.spamhaus.org

What it means

The receiving server rejected the message because the sending IP address or domain is on a spam blocklist.

Common causes

  • The IP address has sent spam – for example from a compromised account or device.
  • Dynamic or residential IP addresses are listed by some blocklists by default.

How to fix it

  1. Check which blocklists list your IP address and follow their delisting process.
  2. Send through your email provider’s submission server rather than directly from your own network.

Tools to help diagnose it

Email blacklist checker

Check whether a mail server IP address or domain is listed on common email blocklists

Email header analyzer

Trace your email’s delivery path and check SPF, DKIM, and DMARC authentication results

SPF, DKIM, and DMARC checker

Check your domain’s email authentication DNS records, count SPF lookups and diagnose deliverability issues

A free tool provided by Auth-Email

Auth-Email makes your Gmail, Outlook, or other OAuth 2.0 email account available to any IMAP, POP3, or SMTP email client — no app passwords or special configuration needed.

Read the docsTry Auth-Email →

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