550 Requested action not taken: mailbox unavailable Reject due to policy restrictions

Reason

HELO settings of your mail system: The acceptance of your emails has been rejected because the HELO used by your mail system is not accepted by us. The two main reasons for this are:

  • Non-resolvable DNS name: The HELO (RFC 5321) used does not correspond to a valid and resolvable DNS name, FQDN (fully qualified domain name). This means that the name cannot be converted into an IP address, which is necessary for the validation of your mail server. Generic names such as "localhost.localdomain" are therefore also not accepted HELOs.
  • Internal HELO blocklist: Your HELO name could also be on our internal block list. This occurs when certain HELO names are blocked due to security issues or cases of abuse.

Solution

Check and change the HELO name of your mail server to ensure that it corresponds to a valid, resolvable DNS name.

If you continue to experience problems despite a valid HELO, please contact us using the contact form provided. Please state the HELO/EHLO you are using so that we can help you specifically.



See also: General information on our error messages.