5xx SMTP error codes

5xx SMTP errors indicate an email could not be delivered due to a permanent problem. You should not retry sending email flagged with a 5xx error. Message delivery can be permanently deferred because:

  • You're trying to send a message to an invalid email address.
  • Spamhaus has your IP address listed on a Block List.
  • Your SMTP connection was rejected.
  • Your message failed authentication checks against your sending domain's DomainKeys or DKIM policy.
  • The message contains characteristics that Yahoo Mail won't accept for policy reasons.

Our recommendations

If you're not the administrator of the mail server in question

Contact your mail server's administrator to discuss the error.

If you're a message content author or mailing policy administrator

If you're seeing this same error consistently over a 48-hour period and you've deployed significant changes attempting to resolve the error, we encourage you to review our recommended best practices when sending to Yahoo Mail.

  • List managers should have a policy for removing email addresses that generate errors/bounces.
  • We review IPs submitted for delivery issues and, based on our review, we may modify your reputation in our systems if needed.
    • Fill out a new sender application if your email is being deferred by Yahoo. This doesn't guarantee inbox delivery.
    • Even if you have a good reputation, users can vote your email as spam and affect your overall reputation.
    • Examine your outbound queues to ensure that spammers aren't abusing your mail server.
    • If you’re using a shared IP address, mail traffic from other domains could be negatively affecting your IP sending reputation. This traffic can result from things outside the sender's control.
  • Consider the following when you review outgoing messages for objectionable content or practices:

Learn how to improve your sender reputation

 Good to know: Yahoo is unable to disclose specific information regarding our filtering practices.

553 SMTP error codes

553 5.7.1 [BLXX] Connections not accepted from IP addresses on Spamhaus [XXX]

If you're seeing one of the error messages below, don't retry sending your message using the same IP address. We suggest you contact Spamhaus. Once your IP is delisted by Spamhaus, Yahoo Mail will automatically unblock your IP within 48 hours.

553 5.7.1 [BL21] Connections not accepted from IP addresses on Spamhaus PBL

Dynamic or residential IP addresses as determined by Spamhaus PBL (Error: 553 5.7.1 [BL21])

The Spamhaus PBL is a DNSBL database of end-user IP address ranges which should not be delivering unauthenticated SMTP email to any Internet mail server except those provided for specifically by an ISP for that customer's use. The PBL helps networks enforce their Acceptable Use Policy for dynamic and non-MTA customer IP ranges.

553 5.7.1 [BL22] Connections not accepted from IP addresses on Spamhaus SBL

IP addresses listed as spam sources on the Spamhaus SBL (Error: 553 5.7.1 [BL22])

The Spamhaus Block List ("SBL") Advisory is a database of IP addresses from which Spamhaus does not recommend the acceptance of electronic mail.

553 5.7.1 [BL23] Connections not accepted from IP addresses on Spamhaus XBL

IP addresses listed as a possible open proxy or spam-sending Trojan Horse on Spamhaus XBL(Error: 553 5.7.1 [BL23])

The Spamhaus Exploits Block List (XBL) is a realtime database of IP addresses of hijacked PCs infected by illegal 3rd party exploits, including open proxies (HTTP, socks, AnalogX, wingate, etc), worms/viruses with built-in spam engines, and other types of trojan-horse exploits.

553 VS99-IP1 deferred

This error means your SMTP connection was rejected. Contact your administrator to resolve this issue.

553 Mail from x.x.x.x not allowed - [numeric code]

The server you use for sending email is configured as an "open relay" or "open proxy."

554 SMTP error codes

554 5.7.1 [MW01] Message content not accepted for policy reasons

This error message indicates that your email wasn't accepted because there is a URL in the message that Yahoo Mail won't accept for policy reasons. For instance, messages with links to viruses or other types of malicious software.

554 5.7.5 (AU01) Message not accepted for policy reasons

This error message indicates that your email wasn't accepted because it failed authentication checks against your sending domain's DomainKeys or DKIM policy. Learn more about what causes this error message.

554 5.7.9: Message not accepted for policy reasons

Yahoo Mail couldn't verify the message came from a legitimate email sender. Learn more about this error and the steps needed to resolve the problem.

554 delivery error: dd This user doesn't have a yahoo.com account ({recipients'userid}@yahoo.com)

The email didn't go through because the recipient's user ID doesn't exist. You shouldn't retry the message, and remove the email address from your list. It will never complete successfully.

554 Message not allowed - [numeric code]

The [numeric code] shows a specific diagnostic code (e.g. "298", "299", "320") in your SMTP logs, and is related to:

  • The date in the message body differs by more than 2 days from the current date.
  • The message contains characteristics that Yahoo Mail won't accept for policy reasons.
    - For example, messages with malicious content or manipulated header information, such as:
    • A falsified origination point.
    • An altered sending date.
    • A forged email address.
    • A URL in the email that is marked as malicious.