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Analyze error codes for undelivered messages

When a message is not delivered to the recipient’s server, two scenarios:

  • The error is final (for example, the recipient’s domain or email does not exist). In this case an error message is sent immediately to the sender.
  • The error is temporary. In this case tries to return the message several times for 24 hours. At the end of this time, if the message is not delivered, an error message is sent to the sender.

In your customer space, you can access mailing reports and view error messages in detail. This is the detailed explanation provided by the recipient’s server during the SMTP transaction.

We have identified the most common error codes:

Definitive errors, the recipient’s email address does not exist.

  • smtp;550 No such recipient here
  • smtp;550 This domain is not in use and does not accept mail
  • smtp;550 5.1.1 The email account that you tried to reach does not exist. Please try double-checking the recipient’s email address for typos or unnecessary spaces. Learn more at r8si11717688wrm.121 – gsmtp
  • smtp;550 Message was not accepted — invalid mailbox. Local mailbox is unavailable: user not found
  • smtp;550 Mailbox not found.
  • smtp;550 No Such User Her
  • smtp;550 Invalid Recipient –
  • smtp;550 user unknown
  • smtp;550 <5.1.1> Recipient address rejected: User unknown in virtual mailbox table
  • smtp;550 #5.1.0 Address rejected.
  • 5.1.2 (bad destination system: no such domain)

Solution: Check your recipient’s email address. Maybe there’s a typo.

Your recipient’s email server or inbox has a problem.

  • 4.4.1 (no answer from host)
  • 5.4.6 (routing loop detected)
  • 4.4.4 (unable to road: dns lookup failure)
  • smtp;550 5.5.0 Requested action not taken: mailbox unavailable. (usually at Outlook 365)
  • smtp;554 delivery error: dd Sorry, your message to cannot be delivered. This mailbox is disabled (554.30). (usually at Yahoo)
  • smtp;550 5.1.1 Address of at least one invalid recipient. Invalid recipient. OFR_416 [416] (Orange)

Solution: In most cases, your recipient’s email address is no longer used. Check with your contact which address they use.

The email is refused due to a problem with the sender

  • smtp;550 Verification failed for Unrouteable address Sender verify failed
    Solution: The sender’s email address does not accept emails. Some anti-spam do this. Avoid using an address of the type

  • smtp;550 5.7.1 spf policy (FAILED)
  • smtp;550 5.7.1 SPF check failed:
  • smtp;550 is not allowed to send mail from (SPF failure)
  • smtp;421 4.7.0 This message does not have authentication information or fails to pass authentication checks. To best protect our users from spam, the message has been blocked. Please visit (Google)
    Solution: Check or set up the SPFs in your sender address’s domain. The procedure is here: configuration of the SPF

  • smtp;550 <5.1.0> Sender address rejected: User unknown in virtual mailbox table
    Solution: The domain name of the sender’s address is the same as that of the recipient’s address. Except that the email address does not exist. If you send an email internally, make it from a valid address.

The email is refused because of the content of the message

  • smtp;554 5.7.1 Spam message rejected
  • x-pmta;bounce-queue;reply:550 5.7.1 [] Our system has detected that this message is likely unsolicited mail. To reduce the amount of spam sent to Gmail, this message has been blocked. Please visit… (Google)
  • smtp;521 5.7.1 Unavailable service; Customer host [] blocked using; Sorry is blacklisted at

Your server sends erroneous mailer-deamon messages to addresses that have never sent it an email.


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