Type: Configuration error (You are often able to resolve this type of error.)
Description: Impersonation of user denied. The connecting Exchange user does not have permission to impersonate the requested resource.
Possible solution: Application impersonation might not be allowed for the connecting Exchange user. Perhaps, a recipient filter that excludes the requested resource might be configured for the application impersonation role.
If the error happens when connecting a service account, please make sure that the service account itself is within the impersonation scope since the validation of the service account is done by impersonating the service account itself.
If the error happens in AskCody Add-ins please try to test if the service account is within the application impersonation scope by going to Connect in Admin Center and press edit on the connection, then updating it without doing changes to the setup. If the update is successful then the impersonation error is for the specific user opening the Add-in. Check if that user mailbox is within the impersonation scope of the service account.
If you are using multiple domains to control multiple connections please make sure that the denied mailbox's domain is added and attached to the correct connection. If it is not attached to the correct domain AskCody will choose the default connection being the first one added.