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Error messages for undeliverable emails

Valid for Mail Basic and Mail Business.

If an email you have sent via IONOS cannot be delivered, you will receive an email containing a status code. This status code informs you of the exact reasons for the non-delivery. The following overview lists these status codes and shows you how you can resolve the issues.

Notes

  • The following status messages relate to emails that you, as a IONOS customer, send to others. Status messages regarding emails sent via external email providers to IONOS customers are explained in the Help Center article SMTP error messages from the IONOS mail servers.
  • Please note that the email issues described and their solutions relate specifically to IONOS. Other email service providers may have different settings.
  • Emails sent by IONOS in the event of non-delivery may contain, in addition to the status code, a link where you can find further details on the reason for non-delivery. We recommend that you also check this information, as it may contain important additional details relevant to your situation.

535 Authentication failure: SMTP AUTH failed with the remote server

Problem:

The username and/or password for your email account at IONOS are incorrect in your email program.

Solution:

Check the settings in your email program. You can find configuration guides for the most common email programs in the IONOS Help Center:

550 Unknown User

Problem:

The email address is unknown.

Solution:

Check the address for typing errors.

Contact the account holder by another means to verify the email address.

550 Action requested not taken: mailbox unavailable

Problem:

The email address does not exist on this server.

Solution:

Check the address for typing errors.

Contact the account holder by another means to verify the email address.

550 Quota Exceeded

Problem:

The email recipient’s inbox is full.

Solution:

Contact the recipient by another means and point this out to them.

550 Your message could not be delivered to all recipients. The following recipients cannot be reached: [...]

Problem:

Your message was not delivered to the recipients listed.

Solution:

There are various reasons for this status message. Please check the following possibilities:

  • Using your own mail server with Dyndns and an internet connection. This is rejected by almost all providers due to the risk of spam abuse.
  • Authentication is required to send emails.
  • SPA authentication must not be enabled in your email program.

554 Service unavailable; Client host [...] blocked via rbl.orbitrbl.com – IP blacklisted

Problem:

The operator of the mail server managing the email address you wrote to has rejected your email due to a blacklist entry.

Solution:

This is usually only a temporary block. Please try sending your email again at a later date.

If your emails are repeatedly rejected, please let us know the details via this contact form. We will then look into finding a solution as soon as possible.

554 Transaction failed, rejected due to policy restrictions

Problem:

The email was rejected by the IONOS SMTP server because it did not comply with the standards defined in RFC 5321 and RFC 5322.

Solution:

The email client must meet the following criteria:

  • The email headers must contain exactly one valid Date line in accordance with RFC 2822.
  • The following header lines must appear only once: From, Sender, To, CC, Subject
  • The headers listed must be syntactically correct

Note: The To and CC lines may contain multiple recipients.

In accordance with the recommendations in RFC 7103, incorrect messages are not automatically corrected by IONOS, as this would otherwise invalidate DKIM signatures. Further information on DKIM signatures can be found in the IONOS article Configuring a DMARC record for a domain.

The domain has no valid mail exchangers

Problem:

The MX records in your DNS settings point to an alias address (CNAME).

Solution:

Adjust your MX records so that they resolve to a unique address.

Status code not listed

Is your status code not listed, or do you need further assistance?

Give us a call

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