Error Messages Caused by Undeliverable Email

If one of your IONOS emails cannot be delivered, you will receive a returned email with a status code. This status code informs you of the exact reasons for the undeliverability. The following overview lists these status codes and shows you ways to eliminate the causes.

Notes
  • The following status messages concern emails that you, as a IONOS customer, send to others. Status messages on emails sent through external email providers to IONOS customers are explained in the Help Center article SMTP Error Messages of the IONOS Mail Servers.
  • Please note that the email problems described and their solutions describe the situation at IONOS. Other email service providers may have different settings and explanations.

535 Authentication Failure: SMTP AUTH Failed with the Remote Server

Problem:

The user name and/or password for your email account at IONOS are incorrectly stored in your email program.

Solution:

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

550 Unknown User

Problem:

The email address is not known.

Solution:

Check the address for typing errors.

Contact the mailbox owner in another way to verify the email address.

550 Requested Action Not Taken: Mailbox Unavailable

Problem:

The email address does not exist on this server.

Solution:

Check the address for typing errors.

Contact the mailbox owner in another way to verify the email address.

550 Quota Exceeded

Problem:

The mailbox of the email recipient is full.

Solution:

Contact the recipient by other means and let them know.

550 Your message could not be delievered to all recipients. The following recipients are not reachable: [...]

Problem:

Your message was not delivered to the listed recipients.

Solution:

There are several reasons for this status message. Check the following options:

  • Own mail server with dyndns and connection to the Internet. This is rejected by almost all providers because of possible spam abuse.
  • Authentication is required for sending emails.
  • SPA authentication must not be activated in your email program.

554 Service unavailable; Client host [...] blocked using rbl.orbitrbl.com - IP Black Listed

Problem:

The operator of the mail server where the email address is administered has rejected your email due to a blacklist entry.

Solution:

Usually this is only a short-term blockage. Send your email again at a later date.

If your emails are rejected repeatedly, please contact IONOS Customer Service.

554 Transaction failed, reject due to policy restrictions

Problem:

The email was rejected by the IONOS SMTP server because the standards defined in RFC 5321 and RFC 5322 were not adhered to.

Solution:

The email client must meet the following criteria:

  • The header lines of the email must contain exactly one valid "Date" line according to RFC 2822.
  • The following header lines may only exist once: From, Sender, To, CC, Subject
  • The header lines mentioned must be syntactically correct

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

In accordance with the recommendations from RFC7103, incorrect messages are not automatically corrected by IONOS, otherwise DKIM signatures become invalid. For more information about DKIM signatures, see the IONOS article Configuring DMARC Records for a Domain.

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.