The email could not be delivered because a temporary error occurred during the DNS MX query of the sender domain.
A prerequisite for the acceptance of an email is that the DNS information for the MX server of the sending domain is available in order to guarantee the possibility of an email response for our customers.
Your email system should automatically attempt to deliver the email again at a later time due to the error code 4xx.It is possible that the problem will no longer occur at this time.
We therefore ask for your patience.
If the problem persists, please check the availability of the DNS infrastructure you are using.