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Bounce Back Error Codes and Messages

Learn how to interpret common email bounce back error codes and messages for Black Pearl Mail.

It is very frustrating to send an email to someone and see the message bounce back. The body of the bounce message may look intimidating, but the text contains an error message that is accompanied by a three-digit error code. We will explain the meaning of the most common bounce messages, show where the problem is located, and how to fix it.

Things to check first


Bounces

There are two bounce types: soft and hard bounces. Hard bounces or the 500s are a ‘no-go’ for that specific email address. The soft bounces or the 400s may succeed later on.

The 500s

A hard bounce is an email message that is returned or bounced back to a sender due to a recipient’s invalid email address and/or domain host details. It is a type of bounced email message that is received only when a sender provides incorrect or unknown email credentials.

Permanent failure is one which is not likely to be resolved by resending the message in the current form. Some change to the message or the destination must be made for successful delivery.

500

  1. What it means - Your message was not delivered because the mailbox it was intended for does not exist.
  2. What to do - Check whether the email address for the recipient is correct or still valid.

501

  1. What it means - A syntax error (i.e. recipient’s email address incorrectly formatted) was encountered in command arguments.
  1. What to do - Check whether the email address for the recipient is correct or still valid.

550

  1. What it means - The message has failed because the recipient’s mailbox is unavailable or because the recipient’s server rejected your message. 
  1. What to do - This error can occur for a number of reasons:
    1. The email address is incorrect or invalid. Check the recipient’s email address.
    2. The recipient’s server rejected the message based on spam filters. Check the content and attachments of your email.
    3. When you auto-forward emails from other organizations (e.g. LinkedIn, Facebook, etc) who have strict DMARC policies - this means you are not allowed to auto-forward these types of emails. Try forwarding the email normally.

551

  1. What it means - Your message was not delivered because the mailbox it was intended for does not exist.
  1. What to do - Check whether the email address for the recipient is correct or still valid.

552

  1. What it means - The mailbox your message was sent to does not have enough storage to accept your message
  1. What to do - Try to resend your email at a later time. If the recipient’s storage has cleared your email will be successfully delivered.

553

  1. What it means - Your message was not delivered because the mailbox it was intended for does not exist.
  1. What to do - Check whether the email address for the recipient is correct or still valid.

554

  1. What it means - This is a very vague message failure response that can refer to any number of problems either on your end or with the recipient’s server.
  1. What to do - This error can occur for a number of reasons:
    1. The email address is incorrect or invalid. Check the recipient’s email address.
    2. The recipient’s server rejected the message based on spam filters. Check the content and attachments of your email.
    3. When you auto-forward emails from other organizations (e.g. LinkedIn, Facebook, etc) who have strict DMARC policies - this means you are not allowed to auto-forward these types of emails. Try forwarding the email normally.

The 400s

A soft bounce refers to an email message that is returned or bounced back due to any temporary availability issue with a recipient’s mailbox or mail/domain server. It is a type of bounced email message that is received only when the recipient is incapable of receiving the message.

It represents that your message experienced the persistence of some temporary condition that has caused abandonment or delay of attempts to send the message. If this code accompanies a delivery failure report, sending in the future may be successful.

421

  1. What it means - Your message was temporarily deferred by the recipient’s server. This is usually a result of the recipient’s mailbox receiving too many emails in a short timeframe. 
  1. What to do - Try to resend your message at a later time. If the recipient is able to receive mail at that time, your message will be delivered.

450

  1. What it means - our message was not delivered because the recipient’s mailbox was not available. This can happen if the mailbox is locked or is not routable.
  1. What to do - Try to resend your message at a later time. If the recipient is able to receive mail at that time, your message will be delivered.

451

  1. What it means - This response is sent when the message simply failed. Often this is not caused by you, but rather because of a far-end server problem.
  1. What to do - Try to resend your message at a later time. If the recipient is able to receive mail at that time, your message will be delivered.

452

  1. What it means - This kind of response is sent when there isn’t enough system storage to receive the message.
  1. What to do - Try to resend your message at a later time. If the recipient is able to receive mail at that time, your message will be delivered.

453

  1. What it means - This indicates a problem with the recipient’s DNS records. The server was either able to get the MX records for the domain but it was unable to connect to any of them, or no MX records were returned for the domain. Standard SMTP practice is to try to connect to the A record of the domain that has no MX records. This has also failed.
  1. What to do - Try to resend your message at a later time. If the recipient is able to receive mail at that time, your message will be delivered.