How to Fix Yahoo SMTP Errors?

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SMTP (Simple Mail Transfer Protocol) is a mechanism that is used between mail servers to exchange emails. All the emails use SMTP to send the messages from the source mail server to the destination mail server.  After the destined mail server receives the message, the user collects it using their client application like Yahoo etc. using POP3 or IMAP protocols.

How to Fix Yahoo SMTP Errors-step-1

Not every SMTP Code is an error. For example, MTP error code 250 means that the message was accepted and the action was complete.

How to Fix Yahoo SMTP Errors-step-2

Below are listed the most common SMTP codes with their causes and possible recommendations.

4xx SMTP Errors

4xx SMTP error is a temporary issue. 4xx SMTP errors indicate that the delivery of the message has been blocked temporarily. Generally these messages are resend by the servers automatically but you can also resend the message after 4 hours of getting the error.

VARIANTS

Some common 4xx SMTP errors codes with their messages are given below:

  • 421 Message temporarily deferred – [numeric code]

The message content contained objectionable content, seen unusual traffic from the mail server or emails from your mail server are generating complaints from Yahoo Mail users.

  • 421 4.7.0 [TS01] Messages from x.x.x.x temporarily deferred due to user complaints – 4.16.55

Seen unusual traffic patterns from the mail server.

  • 421 4.7.0 [TS02] Messages from x.x.x.x temporarily deferred due to user complaints – 4.16.55

Seen unusual traffic patterns from the mail server or your mailings are generating complaints from Yahoo Mail users. Submit your sending IPs for review.

  • 421 4.7.1 [TS03] Messages from x.x.x.x permanently deferred. Retrying will NOT succeed

A high volume of e-mails from the mail server has been seen that is indicative of unsolicited mailings. Submit your sending IPs for review.

  • 451 Resources temporarily not available – Please try again later [numeric code]

This error indicates that our servers were busy and unable to process your transaction temporarily at the time of connection.

  • 451 VS1-IP Excessive unknown recipients – possible Open Relay (#4.1.8)

Your mail server is configured as an open relay or proxy.

  • 451 VS1-MF Excessive unknown recipients – possible Open Relay (#4.4.5)

The sender’s MAIL FROM address has been sending to excessive bouncing accounts (non-active, don’t exist). Review your mailing lists and remove any address that generates bounces.

CAUSES:

The possible causes behind these 4xx SMTP errors could be:

  • Yahoo mail server has observed unusual traffic patterns from the sending mail server’s IP address.
  • The message you wanted to send looks like a spam message.
  • Emails from sending mail server have been getting complaints from Yahoo Mail users.
  • Connection could not be established because Yahoo Mail servers were busy.

RECOMMENDATIONS:

The best practice to make sure that your message is delivered is to avoid looking like a spammer. If you have made necessary changes to the message in order to resolve the error, but the error continues even after 48 hours, you should review the following points before sending any mail to reach out to the Yahoo audience.

  • Errors with 4xx messages are the temporary errors, so you can try resending them.
  • If you sign your emails with DKIM or Domain Keys, you can track and manage your spam complaint rates using Yahoo’s Complaint Feedback Loop program.
  • Try including DKIM authenticated signatures in your emails. DKIM signature helps Yahoo to authenticate that email is safe, secure and from the original sender. If the email is not being DKIM signed, it may appear to be sent by a spammer.
  • Yahoo generally downgrades an IP’s sending reputation if there is no reverse DNS entry for the IP address or if the mailing IP looks like a dynamically assigned IP address instead of a static mail server.
  • You should always adhere to the requirements specified by the CAN-SPAM Act.

 

5xx SMTP Errors

A 5xx error indicates a permanent failure. You should not send an email again that comes back with this kind of error. 5xx SMTP errors indicate that the email could not be delivered due to a permanent problem.

VARIANTS

Some common 5xx SMTP errors codes with their messages are given below:

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

If any of the below given error occurs, do not send your message again with the same IP address. Yahoo Mail will automatically unblock your IP within 48 hours once your IP is delisted by Spamhaus.

  • 553 5.7.1 [BL21] Connections not accepted from IP addresses on Spamhaus PBL
  • 553 5.7.1 [BL22] Connections not accepted from IP addresses on Spamhaus SBL
  • 553 5.7.1 [BL23] Connections not accepted from IP addresses on Spamhaus XBL
  • 553 VS99-IP1 deferred

This error code means that your SMTP connection was rejected by the mail server and you should contact your administrator to solve this issue.

  • 553 Mail from x.x.x.x not allowed – [numeric code]

The mail server you have used for sending the email is configured as an “open relay” or “open proxy.”

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

This error code means that your email was not accepted because your email contains a URL that is not acceptable to Yahoo Mail as policy reasons. These could be 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

This error code means that the Yahoo Mail could not verify that the message was sent by a legitimate email sender.

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

This email delivery was not possible because the recipient’s user ID doesn’t exist.

  • 554 Message not allowed – [numeric code]

The [numeric code] shows a specific diagnostic code (e.g. “298”, “299”, “320”) in the 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 some characteristics that Yahoo Mail would not accept for policy reasons like malicious content, manipulated header information etc.

 CAUSES:

The message delivery can be permanently deferred because of the following reasons:

  • You are sending an email to an invalid email address.
  • Your IP address has been listed on a Block List.
  • The SMTP connection was rejected.
  • Your message failed authentication checks against your sending domain’s DomainKeys or DKIM policy.
  • The message contains any link or content that Yahoo Mail can’t accept due to policy reasons.

 RECOMMENDATIONS:

  • Yahoo reviews the IP addresses submitted for delivery issues and can modify your reputation in their systems if required according to the review.
  • You have the option to fill out a new sender application form if your email is being deferred by Yahoo.
  • Users can vote your email as spam and harm your overall reputation even if you already have a good reputation.
  • Keep a check on your outbound queues to ensure that spammers are not misusing your mail server.
  • If you are using a shared IP address, the email traffic from other domains can also be negatively affecting your IP sending reputation.
  • You should keep in mind the following while reviewing outgoing messages for any objectionable content or practice:
  • IP address reputation.
  • URL reputation.
  • Sender reputation.
  • Domain reputation.
  • DomainKeys Identified Mail (DKIM) signatures.
  • Domain-based Message Authentication, Reporting & Conformance (DMARC) authentication
  • Perform list management tasks on a frequent basis.
  • Send email only to those who want to receive it like sending newsletters, subscriptions etc.
  • Review email content to avoid spam.
  • Have separate IP addresses and streams depending on your email content type.
  • Secure your email servers by updating your software with latest features, using filters etc.
  • Review SMTP reply codes often and do not retry sending mails with the 5xx codes.
  • Make sure to always include DKIM authenticated signatures in your emails.
  • Yahoo is more likely to downgrade an IP’s sending reputation if:
    1. There’s no reverse DNS entry for your IP address.
    2. Your mailing IP looks like a dynamically-assigned IP instead of a static mail server.Be CAN-SPAM and DMARC compliant.

 

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