The following non-delivery report:

This message hasn't been delivered yet. Delivery will continue to be attempted.
The message hasn't been delivered yet

means that the sending server is trying to connect to the recipient server but is unable to do so and will continue to attempt the delivery for a certain period of time. You will see the remaining time in the text of the bounce back message.

The Diagnostic information for administrators section also contains the following error:

Remote Server returned '400 4.4.7 Message delayed'Message delayed

When Exchange server cannot send the message immediately, it continues to attempt delivery for another 24 hours. If the attempts are failing during that period of time, you will be receiving the bounce back messages above.

Communication issues between two servers can be caused by a variety of different reasons, such as:

  • the inability to resolve the MX records of the recipient domain properly. Check if the MX records of the recipient domain can be resolved using a public DNS lookup tool. If you are the sender and they exist, contact Support and provide them with the full bounce back message. If it does not or is not fully propagated, contact the recipient directly.
  • the A or MX records for the sender's domain do not exist or are not fully propagated. Most mail servers do not accept mail from the domains without valid A or MX records. Check if they can be resolved using a public DNS lookup tool. If you are the sender and they cannot be resolved, contact your DNS hosting provider. If they can be resolved, contact Support and provide them with the full bounce back message so that Intermedia could determine the root cause of the delay.
  • the IP address of the recipient server is added to a blacklist. Check if that is the case using a public blacklist lookup tool. If it is and you are the sender, contact the recipient direcly so that they could address this issue.
  • the IP address of the sending server is blacklisted on the recipient side. Contact the recipient directly to check if that is the case. If the recipient administrator requires SMTP send logs from the sender's side, contact Support and provide them with the full bounce back message
  • the IP address of the sending server is added to a blacklist. Check if that is the case using a public blacklist lookup tool. If it is and you are the sender, contact Support and provide them with the full bounce back message.