List owners may receive an error message that reads:

>> The enclosed  message, found in  the listname mailbox and shown  under the spool ID xxxx  in the system log,  has been identified as  a possible delivery error notice for the following reason: "X-Report-Type:" field found in the mail header

The list owner should click on the attachment included with this message. The attachment will give them more information about the specific error.

The attachment may read:

This is an automatically generated Delivery Status Notification.
Delivery to the following recipients failed.
janedoe@example.com

In this example, the attachment tells the list owner that the message was unable to be delivered to the recipient. This could be because the subscriber is over quota or the address is no longer valid. If the list owner continues to receive this error message, it is best to remove the subscriber from the list.

This error message occurs when a message cannot be delivered to one or more recipients. The recipient's email address may be incorrect